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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-16) exists of draft-ietf-ace-oauth-params-13 ** Downref: Normative reference to an Informational RFC: RFC 4949 ** Obsolete normative reference: RFC 6347 (Obsoleted by RFC 9147) ** Obsolete normative reference: RFC 7049 (Obsoleted by RFC 8949) == Outdated reference: draft-ietf-quic-transport has been published as RFC 9000 == Outdated reference: draft-ietf-tls-dtls13 has been published as RFC 9147 Summary: 3 errors (**), 0 flaws (~~), 4 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 ACE Working Group L. Seitz 3 Internet-Draft Combitech 4 Intended status: Standards Track G. Selander 5 Expires: May 21, 2021 Ericsson 6 E. Wahlstroem 8 S. Erdtman 9 Spotify AB 10 H. Tschofenig 11 Arm Ltd. 12 November 17, 2020 14 Authentication and Authorization for Constrained Environments (ACE) 15 using the OAuth 2.0 Framework (ACE-OAuth) 16 draft-ietf-ace-oauth-authz-36 18 Abstract 20 This specification defines a framework for authentication and 21 authorization in Internet of Things (IoT) environments called ACE- 22 OAuth. The framework is based on a set of building blocks including 23 OAuth 2.0 and the Constrained Application Protocol (CoAP), thus 24 transforming a well-known and widely used authorization solution into 25 a form suitable for IoT devices. Existing specifications are used 26 where possible, but extensions are added and profiles are defined to 27 better serve the IoT use cases. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at https://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on May 21, 2021. 46 Copyright Notice 48 Copyright (c) 2020 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (https://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 64 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 65 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 6 66 3.1. OAuth 2.0 . . . . . . . . . . . . . . . . . . . . . . . . 7 67 3.2. CoAP . . . . . . . . . . . . . . . . . . . . . . . . . . 10 68 4. Protocol Interactions . . . . . . . . . . . . . . . . . . . . 11 69 5. Framework . . . . . . . . . . . . . . . . . . . . . . . . . . 15 70 5.1. Discovering Authorization Servers . . . . . . . . . . . . 16 71 5.2. Unauthorized Resource Request Message . . . . . . . . . . 17 72 5.3. AS Request Creation Hints . . . . . . . . . . . . . . . . 17 73 5.3.1. The Client-Nonce Parameter . . . . . . . . . . . . . 19 74 5.4. Authorization Grants . . . . . . . . . . . . . . . . . . 20 75 5.5. Client Credentials . . . . . . . . . . . . . . . . . . . 21 76 5.6. AS Authentication . . . . . . . . . . . . . . . . . . . . 21 77 5.7. The Authorization Endpoint . . . . . . . . . . . . . . . 21 78 5.8. The Token Endpoint . . . . . . . . . . . . . . . . . . . 21 79 5.8.1. Client-to-AS Request . . . . . . . . . . . . . . . . 22 80 5.8.2. AS-to-Client Response . . . . . . . . . . . . . . . . 25 81 5.8.3. Error Response . . . . . . . . . . . . . . . . . . . 27 82 5.8.4. Request and Response Parameters . . . . . . . . . . . 28 83 5.8.4.1. Grant Type . . . . . . . . . . . . . . . . . . . 28 84 5.8.4.2. Token Type . . . . . . . . . . . . . . . . . . . 29 85 5.8.4.3. Profile . . . . . . . . . . . . . . . . . . . . . 29 86 5.8.4.4. Client-Nonce . . . . . . . . . . . . . . . . . . 30 87 5.8.5. Mapping Parameters to CBOR . . . . . . . . . . . . . 30 88 5.9. The Introspection Endpoint . . . . . . . . . . . . . . . 31 89 5.9.1. Introspection Request . . . . . . . . . . . . . . . . 32 90 5.9.2. Introspection Response . . . . . . . . . . . . . . . 33 91 5.9.3. Error Response . . . . . . . . . . . . . . . . . . . 34 92 5.9.4. Mapping Introspection parameters to CBOR . . . . . . 35 93 5.10. The Access Token . . . . . . . . . . . . . . . . . . . . 35 94 5.10.1. The Authorization Information Endpoint . . . . . . . 36 95 5.10.1.1. Verifying an Access Token . . . . . . . . . . . 37 96 5.10.1.2. Protecting the Authorization Information 97 Endpoint . . . . . . . . . . . . . . . . . . . . 39 98 5.10.2. Client Requests to the RS . . . . . . . . . . . . . 39 99 5.10.3. Token Expiration . . . . . . . . . . . . . . . . . . 40 100 5.10.4. Key Expiration . . . . . . . . . . . . . . . . . . . 41 101 6. Security Considerations . . . . . . . . . . . . . . . . . . . 42 102 6.1. Protecting Tokens . . . . . . . . . . . . . . . . . . . . 42 103 6.2. Communication Security . . . . . . . . . . . . . . . . . 43 104 6.3. Long-Term Credentials . . . . . . . . . . . . . . . . . . 44 105 6.4. Unprotected AS Request Creation Hints . . . . . . . . . . 44 106 6.5. Minimal security requirements for communication . 45 107 6.6. Token Freshness and Expiration . . . . . . . . . . . . . 46 108 6.7. Combining profiles . . . . . . . . . . . . . . . . . . . 46 109 6.8. Unprotected Information . . . . . . . . . . . . . . . . . 47 110 6.9. Identifying audiences . . . . . . . . . . . . . . . . . . 47 111 6.10. Denial of service against or with Introspection . . 48 112 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 49 113 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 50 114 8.1. ACE Authorization Server Request Creation Hints . . . . . 50 115 8.2. CoRE Resource Type registry . . . . . . . . . . . . . . . 50 116 8.3. OAuth Extensions Error Registration . . . . . . . . . . . 51 117 8.4. OAuth Error Code CBOR Mappings Registry . . . . . . . . . 51 118 8.5. OAuth Grant Type CBOR Mappings . . . . . . . . . . . . . 51 119 8.6. OAuth Access Token Types . . . . . . . . . . . . . . . . 52 120 8.7. OAuth Access Token Type CBOR Mappings . . . . . . . . . . 52 121 8.7.1. Initial Registry Contents . . . . . . . . . . . . . . 53 122 8.8. ACE Profile Registry . . . . . . . . . . . . . . . . . . 53 123 8.9. OAuth Parameter Registration . . . . . . . . . . . . . . 53 124 8.10. OAuth Parameters CBOR Mappings Registry . . . . . . . . . 54 125 8.11. OAuth Introspection Response Parameter Registration . . . 54 126 8.12. OAuth Token Introspection Response CBOR Mappings Registry 55 127 8.13. JSON Web Token Claims . . . . . . . . . . . . . . . . . . 55 128 8.14. CBOR Web Token Claims . . . . . . . . . . . . . . . . . . 56 129 8.15. Media Type Registrations . . . . . . . . . . . . . . . . 57 130 8.16. CoAP Content-Format Registry . . . . . . . . . . . . . . 57 131 8.17. Expert Review Instructions . . . . . . . . . . . . . . . 58 132 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 59 133 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 59 134 10.1. Normative References . . . . . . . . . . . . . . . . . . 59 135 10.2. Informative References . . . . . . . . . . . . . . . . . 62 136 Appendix A. Design Justification . . . . . . . . . . . . . . . . 64 137 Appendix B. Roles and Responsibilities . . . . . . . . . . . . . 68 138 Appendix C. Requirements on Profiles . . . . . . . . . . . . . . 70 139 Appendix D. Assumptions on AS knowledge about C and RS . . . . . 71 140 Appendix E. Deployment Examples . . . . . . . . . . . . . . . . 72 141 E.1. Local Token Validation . . . . . . . . . . . . . . . . . 72 142 E.2. Introspection Aided Token Validation . . . . . . . . . . 76 143 Appendix F. Document Updates . . . . . . . . . . . . . . . . . . 80 144 F.1. Version -21 to 22 . . . . . . . . . . . . . . . . . . . . 81 145 F.2. Version -20 to 21 . . . . . . . . . . . . . . . . . . . . 81 146 F.3. Version -19 to 20 . . . . . . . . . . . . . . . . . . . . 81 147 F.4. Version -18 to -19 . . . . . . . . . . . . . . . . . . . 81 148 F.5. Version -17 to -18 . . . . . . . . . . . . . . . . . . . 81 149 F.6. Version -16 to -17 . . . . . . . . . . . . . . . . . . . 81 150 F.7. Version -15 to -16 . . . . . . . . . . . . . . . . . . . 82 151 F.8. Version -14 to -15 . . . . . . . . . . . . . . . . . . . 82 152 F.9. Version -13 to -14 . . . . . . . . . . . . . . . . . . . 82 153 F.10. Version -12 to -13 . . . . . . . . . . . . . . . . . . . 82 154 F.11. Version -11 to -12 . . . . . . . . . . . . . . . . . . . 83 155 F.12. Version -10 to -11 . . . . . . . . . . . . . . . . . . . 83 156 F.13. Version -09 to -10 . . . . . . . . . . . . . . . . . . . 83 157 F.14. Version -08 to -09 . . . . . . . . . . . . . . . . . . . 83 158 F.15. Version -07 to -08 . . . . . . . . . . . . . . . . . . . 83 159 F.16. Version -06 to -07 . . . . . . . . . . . . . . . . . . . 84 160 F.17. Version -05 to -06 . . . . . . . . . . . . . . . . . . . 84 161 F.18. Version -04 to -05 . . . . . . . . . . . . . . . . . . . 84 162 F.19. Version -03 to -04 . . . . . . . . . . . . . . . . . . . 85 163 F.20. Version -02 to -03 . . . . . . . . . . . . . . . . . . . 85 164 F.21. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 85 165 F.22. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 86 166 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 86 168 1. Introduction 170 Authorization is the process for granting approval to an entity to 171 access a generic resource [RFC4949]. The authorization task itself 172 can best be described as granting access to a requesting client, for 173 a resource hosted on a device, the resource server (RS). This 174 exchange is mediated by one or multiple authorization servers (AS). 175 Managing authorization for a large number of devices and users can be 176 a complex task. 178 While prior work on authorization solutions for the Web and for the 179 mobile environment also applies to the Internet of Things (IoT) 180 environment, many IoT devices are constrained, for example, in terms 181 of processing capabilities, available memory, etc. For web 182 applications on constrained nodes, this specification RECOMMENDS the 183 use of the Constrained Application Protocol (CoAP) [RFC7252] as 184 replacement for HTTP. 186 Appendix A gives an overview of the constraints considered in this 187 design, and a more detailed treatment of constraints can be found in 188 [RFC7228]. This design aims to accommodate different IoT deployments 189 and thus a continuous range of device and network capabilities. 191 Taking energy consumption as an example: At one end there are energy- 192 harvesting or battery powered devices which have a tight power 193 budget, on the other end there are mains-powered devices, and all 194 levels in between. 196 Hence, IoT devices may be very different in terms of available 197 processing and message exchange capabilities and there is a need to 198 support many different authorization use cases [RFC7744]. 200 This specification describes a framework for authentication and 201 authorization in constrained environments (ACE) built on re-use of 202 OAuth 2.0 [RFC6749], thereby extending authorization to Internet of 203 Things devices. This specification contains the necessary building 204 blocks for adjusting OAuth 2.0 to IoT environments. 206 More detailed, interoperable specifications can be found in separate 207 profile specifications. Implementations may claim conformance with a 208 specific profile, whereby implementations utilizing the same profile 209 interoperate while implementations of different profiles are not 210 expected to be interoperable. Some devices, such as mobile phones 211 and tablets, may implement multiple profiles and will therefore be 212 able to interact with a wider range of low end devices. Requirements 213 on profiles are described at contextually appropriate places 214 throughout this specification, and also summarized in Appendix C. 216 2. Terminology 218 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 219 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 220 "OPTIONAL" in this document are to be interpreted as described in BCP 221 14 [RFC2119] [RFC8174] when, and only when, they appear in all 222 capitals, as shown here. 224 Certain security-related terms such as "authentication", 225 "authorization", "confidentiality", "(data) integrity", "message 226 authentication code", and "verify" are taken from [RFC4949]. 228 Since exchanges in this specification are described as RESTful 229 protocol interactions, HTTP [RFC7231] offers useful terminology. 231 Terminology for entities in the architecture is defined in OAuth 2.0 232 [RFC6749] such as client (C), resource server (RS), and authorization 233 server (AS). 235 Note that the term "endpoint" is used here following its OAuth 236 definition, which is to denote resources such as token and 237 introspection at the AS and authz-info at the RS (see Section 5.10.1 238 for a definition of the authz-info endpoint). The CoAP [RFC7252] 239 definition, which is "An entity participating in the CoAP protocol" 240 is not used in this specification. 242 The specifications in this document is called the "framework" or "ACE 243 framework". When referring to "profiles of this framework" it refers 244 to additional specifications that define the use of this 245 specification with concrete transport and communication security 246 protocols (e.g., CoAP over DTLS). 248 We use the term "Access Information" for parameters other than the 249 access token provided to the client by the AS to enable it to access 250 the RS (e.g. public key of the RS, profile supported by RS). 252 We use the term "Authorization Information" to denote all 253 information, including the claims of relevant access tokens, that an 254 RS uses to determine whether an access request should be granted. 256 3. Overview 258 This specification defines the ACE framework for authorization in the 259 Internet of Things environment. It consists of a set of building 260 blocks. 262 The basic block is the OAuth 2.0 [RFC6749] framework, which enjoys 263 widespread deployment. Many IoT devices can support OAuth 2.0 264 without any additional extensions, but for certain constrained 265 settings additional profiling is needed. 267 Another building block is the lightweight web transfer protocol CoAP 268 [RFC7252], for those communication environments where HTTP is not 269 appropriate. CoAP typically runs on top of UDP, which further 270 reduces overhead and message exchanges. While this specification 271 defines extensions for the use of OAuth over CoAP, other underlying 272 protocols are not prohibited from being supported in the future, such 273 as HTTP/2 [RFC7540], Message Queuing Telemetry Transport (MQTT) 274 [MQTT5.0], Bluetooth Low Energy (BLE) [BLE] and QUIC 275 [I-D.ietf-quic-transport]. Note that this document specifies 276 protocol exchanges in terms of RESTful verbs such as GET and POST. 277 Future profiles using protocols that do not support these verbs MUST 278 specify how the corresponding protocol messages are transmitted 279 instead. 281 A third building block is the Concise Binary Object Representation 282 (CBOR) [RFC7049], for encodings where JSON [RFC8259] is not 283 sufficiently compact. CBOR is a binary encoding designed for small 284 code and message size, which may be used for encoding of self 285 contained tokens, and also for encoding payloads transferred in 286 protocol messages. 288 A fourth building block is CBOR Object Signing and Encryption (COSE) 289 [RFC8152], which enables object-level layer security as an 290 alternative or complement to transport layer security (DTLS [RFC6347] 291 or TLS [RFC8446]). COSE is used to secure self-contained tokens such 292 as proof-of-possession (PoP) tokens, which are an extension to the 293 OAuth bearer tokens. The default token format is defined in CBOR web 294 token (CWT) [RFC8392]. Application layer security for CoAP using 295 COSE can be provided with OSCORE [RFC8613]. 297 With the building blocks listed above, solutions satisfying various 298 IoT device and network constraints are possible. A list of 299 constraints is described in detail in [RFC7228] and a description of 300 how the building blocks mentioned above relate to the various 301 constraints can be found in Appendix A. 303 Luckily, not every IoT device suffers from all constraints. The ACE 304 framework nevertheless takes all these aspects into account and 305 allows several different deployment variants to co-exist, rather than 306 mandating a one-size-fits-all solution. It is important to cover the 307 wide range of possible interworking use cases and the different 308 requirements from a security point of view. Once IoT deployments 309 mature, popular deployment variants will be documented in the form of 310 ACE profiles. 312 3.1. OAuth 2.0 314 The OAuth 2.0 authorization framework enables a client to obtain 315 scoped access to a resource with the permission of a resource owner. 316 Authorization information, or references to it, is passed between the 317 nodes using access tokens. These access tokens are issued to clients 318 by an authorization server with the approval of the resource owner. 319 The client uses the access token to access the protected resources 320 hosted by the resource server. 322 A number of OAuth 2.0 terms are used within this specification: 324 The token and introspection Endpoints: 325 The AS hosts the token endpoint that allows a client to request 326 access tokens. The client makes a POST request to the token 327 endpoint on the AS and receives the access token in the response 328 (if the request was successful). 329 In some deployments, a token introspection endpoint is provided by 330 the AS, which can be used by the RS if it needs to request 331 additional information regarding a received access token. The RS 332 makes a POST request to the introspection endpoint on the AS and 333 receives information about the access token in the response. (See 334 "Introspection" below.) 336 Access Tokens: 337 Access tokens are credentials needed to access protected 338 resources. An access token is a data structure representing 339 authorization permissions issued by the AS to the client. Access 340 tokens are generated by the AS and consumed by the RS. The access 341 token content is opaque to the client. 343 Access tokens can have different formats, and various methods of 344 utilization e.g., cryptographic properties) based on the security 345 requirements of the given deployment. 347 Refresh Tokens: 348 Refresh tokens are credentials used to obtain access tokens. 349 Refresh tokens are issued to the client by the authorization 350 server and are used to obtain a new access token when the current 351 access token becomes invalid or expires, or to obtain additional 352 access tokens with identical or narrower scope (such access tokens 353 may have a shorter lifetime and fewer permissions than authorized 354 by the resource owner). Issuing a refresh token is optional at 355 the discretion of the authorization server. If the authorization 356 server issues a refresh token, it is included when issuing an 357 access token (i.e., step (B) in Figure 1). 359 A refresh token in OAuth 2.0 is a string representing the 360 authorization granted to the client by the resource owner. The 361 string is usually opaque to the client. The token denotes an 362 identifier used to retrieve the authorization information. Unlike 363 access tokens, refresh tokens are intended for use only with 364 authorization servers and are never sent to resource servers. In 365 this framework, refresh tokens are encoded in binary instead of 366 strings, if used. 368 Proof of Possession Tokens: 369 A token may be bound to a cryptographic key, which is then used to 370 bind the token to a request authorized by the token. Such tokens 371 are called proof-of-possession tokens (or PoP tokens). 373 The proof-of-possession (PoP) security concept used here assumes 374 that the AS acts as a trusted third party that binds keys to 375 tokens. In the case of access tokens, these so called PoP keys 376 are then used by the client to demonstrate the possession of the 377 secret to the RS when accessing the resource. The RS, when 378 receiving an access token, needs to verify that the key used by 379 the client matches the one bound to the access token. When this 380 specification uses the term "access token" it is assumed to be a 381 PoP access token token unless specifically stated otherwise. 383 The key bound to the token (the PoP key) may use either symmetric 384 or asymmetric cryptography. The appropriate choice of the kind of 385 cryptography depends on the constraints of the IoT devices as well 386 as on the security requirements of the use case. 388 Symmetric PoP key: 389 The AS generates a random symmetric PoP key. The key is either 390 stored to be returned on introspection calls or encrypted and 391 included in the token. The PoP key is also encrypted for the 392 token recipient and sent to the recipient together with the 393 token. 395 Asymmetric PoP key: 396 An asymmetric key pair is generated on the token's recipient 397 and the public key is sent to the AS (if it does not already 398 have knowledge of the recipient's public key). Information 399 about the public key, which is the PoP key in this case, is 400 either stored to be returned on introspection calls or included 401 inside the token and sent back to the requesting party. The 402 consumer of the token can identify the public key from the 403 information in the token, which allows the recipient of the 404 token to use the corresponding private key for the proof of 405 possession. 407 The token is either a simple reference, or a structured 408 information object (e.g., CWT [RFC8392]) protected by a 409 cryptographic wrapper (e.g., COSE [RFC8152]). The choice of PoP 410 key does not necessarily imply a specific credential type for the 411 integrity protection of the token. 413 Scopes and Permissions: 414 In OAuth 2.0, the client specifies the type of permissions it is 415 seeking to obtain (via the scope parameter) in the access token 416 request. In turn, the AS may use the scope response parameter to 417 inform the client of the scope of the access token issued. As the 418 client could be a constrained device as well, this specification 419 defines the use of CBOR encoding, see Section 5, for such requests 420 and responses. 422 The values of the scope parameter in OAuth 2.0 are expressed as a 423 list of space-delimited, case-sensitive strings, with a semantic 424 that is well-known to the AS and the RS. More details about the 425 concept of scopes is found under Section 3.3 in [RFC6749]. 427 Claims: 428 Information carried in the access token or returned from 429 introspection, called claims, is in the form of name-value pairs. 430 An access token may, for example, include a claim identifying the 431 AS that issued the token (via the "iss" claim) and what audience 432 the access token is intended for (via the "aud" claim). The 433 audience of an access token can be a specific resource or one or 434 many resource servers. The resource owner policies influence what 435 claims are put into the access token by the authorization server. 437 While the structure and encoding of the access token varies 438 throughout deployments, a standardized format has been defined 439 with the JSON Web Token (JWT) [RFC7519] where claims are encoded 440 as a JSON object. In [RFC8392], an equivalent format using CBOR 441 encoding (CWT) has been defined. 443 Introspection: 444 Introspection is a method for a resource server to query the 445 authorization server for the active state and content of a 446 received access token. This is particularly useful in those cases 447 where the authorization decisions are very dynamic and/or where 448 the received access token itself is an opaque reference rather 449 than a self-contained token. More information about introspection 450 in OAuth 2.0 can be found in [RFC7662]. 452 3.2. CoAP 454 CoAP is an application layer protocol similar to HTTP, but 455 specifically designed for constrained environments. CoAP typically 456 uses datagram-oriented transport, such as UDP, where reordering and 457 loss of packets can occur. A security solution needs to take the 458 latter aspects into account. 460 While HTTP uses headers and query strings to convey additional 461 information about a request, CoAP encodes such information into 462 header parameters called 'options'. 464 CoAP supports application-layer fragmentation of the CoAP payloads 465 through blockwise transfers [RFC7959]. However, blockwise transfer 466 does not increase the size limits of CoAP options, therefore data 467 encoded in options has to be kept small. 469 Transport layer security for CoAP can be provided by DTLS or TLS 470 [RFC6347][RFC8446] [I-D.ietf-tls-dtls13]. CoAP defines a number of 471 proxy operations that require transport layer security to be 472 terminated at the proxy. One approach for protecting CoAP 473 communication end-to-end through proxies, and also to support 474 security for CoAP over a different transport in a uniform way, is to 475 provide security at the application layer using an object-based 476 security mechanism such as COSE [RFC8152]. 478 One application of COSE is OSCORE [RFC8613], which provides end-to- 479 end confidentiality, integrity and replay protection, and a secure 480 binding between CoAP request and response messages. In OSCORE, the 481 CoAP messages are wrapped in COSE objects and sent using CoAP. 483 This framework RECOMMENDS the use of CoAP as replacement for HTTP for 484 use in constrained environments. For communication security this 485 framework does not make an explicit protocol recommendation, since 486 the choice depends on the requirements of the specific application. 487 DTLS [RFC6347], [I-D.ietf-tls-dtls13] and OSCORE [RFC8613] are 488 mentioned as examples, other protocols fulfilling the requirements 489 from Section 6.5 are also applicable. 491 4. Protocol Interactions 493 The ACE framework is based on the OAuth 2.0 protocol interactions 494 using the token endpoint and optionally the introspection endpoint. 495 A client obtains an access token, and optionally a refresh token, 496 from an AS using the token endpoint and subsequently presents the 497 access token to an RS to gain access to a protected resource. In 498 most deployments the RS can process the access token locally, however 499 in some cases the RS may present it to the AS via the introspection 500 endpoint to get fresh information. These interactions are shown in 501 Figure 1. An overview of various OAuth concepts is provided in 502 Section 3.1. 504 The OAuth 2.0 framework defines a number of "protocol flows" via 505 grant types, which have been extended further with extensions to 506 OAuth 2.0 (such as [RFC7521] and [RFC8628]). What grant types works 507 best depends on the usage scenario and [RFC7744] describes many 508 different IoT use cases but there are two preferred grant types, 509 namely the Authorization Code Grant (described in Section 4.1 of 510 [RFC7521]) and the Client Credentials Grant (described in Section 4.4 511 of [RFC7521]). The Authorization Code Grant is a good fit for use 512 with apps running on smart phones and tablets that request access to 513 IoT devices, a common scenario in the smart home environment, where 514 users need to go through an authentication and authorization phase 515 (at least during the initial setup phase). The native apps 516 guidelines described in [RFC8252] are applicable to this use case. 517 The Client Credential Grant is a good fit for use with IoT devices 518 where the OAuth client itself is constrained. In such a case, the 519 resource owner has pre-arranged access rights for the client with the 520 authorization server, which is often accomplished using a 521 commissioning tool. 523 The consent of the resource owner, for giving a client access to a 524 protected resource, can be provided dynamically as in the traditional 525 OAuth flows, or it could be pre-configured by the resource owner as 526 authorization policies at the AS, which the AS evaluates when a token 527 request arrives. The resource owner and the requesting party (i.e., 528 client owner) are not shown in Figure 1. 530 This framework supports a wide variety of communication security 531 mechanisms between the ACE entities, such as client, AS, and RS. It 532 is assumed that the client has been registered (also called enrolled 533 or onboarded) to an AS using a mechanism defined outside the scope of 534 this document. In practice, various techniques for onboarding have 535 been used, such as factory-based provisioning or the use of 536 commissioning tools. Regardless of the onboarding technique, this 537 provisioning procedure implies that the client and the AS exchange 538 credentials and configuration parameters. These credentials are used 539 to mutually authenticate each other and to protect messages exchanged 540 between the client and the AS. 542 It is also assumed that the RS has been registered with the AS, 543 potentially in a similar way as the client has been registered with 544 the AS. Established keying material between the AS and the RS allows 545 the AS to apply cryptographic protection to the access token to 546 ensure that its content cannot be modified, and if needed, that the 547 content is confidentiality protected. 549 The keying material necessary for establishing communication security 550 between C and RS is dynamically established as part of the protocol 551 described in this document. 553 At the start of the protocol, there is an optional discovery step 554 where the client discovers the resource server and the resources this 555 server hosts. In this step, the client might also determine what 556 permissions are needed to access the protected resource. A generic 557 procedure is described in Section 5.1; profiles MAY define other 558 procedures for discovery. 560 In Bluetooth Low Energy, for example, advertisements are broadcasted 561 by a peripheral, including information about the primary services. 563 In CoAP, as a second example, a client can make a request to "/.well- 564 known/core" to obtain information about available resources, which 565 are returned in a standardized format as described in [RFC6690]. 567 +--------+ +---------------+ 568 | |---(A)-- Token Request ------->| | 569 | | | Authorization | 570 | |<--(B)-- Access Token ---------| Server | 571 | | + Access Information | | 572 | | + Refresh Token (optional) +---------------+ 573 | | ^ | 574 | | Introspection Request (D)| | 575 | Client | (optional) | | 576 | | Response | |(E) 577 | | (optional) | v 578 | | +--------------+ 579 | |---(C)-- Token + Request ----->| | 580 | | | Resource | 581 | |<--(F)-- Protected Resource ---| Server | 582 | | | | 583 +--------+ +--------------+ 585 Figure 1: Basic Protocol Flow. 587 Requesting an Access Token (A): 588 The client makes an access token request to the token endpoint at 589 the AS. This framework assumes the use of PoP access tokens (see 590 Section 3.1 for a short description) wherein the AS binds a key to 591 an access token. The client may include permissions it seeks to 592 obtain, and information about the credentials it wants to use 593 (e.g., symmetric/asymmetric cryptography or a reference to a 594 specific credential). 596 Access Token Response (B): 597 If the AS successfully processes the request from the client, it 598 returns an access token and optionally a refresh token (note that 599 only certain grant types support refresh tokens). It can also 600 return additional parameters, referred to as "Access Information". 601 In addition to the response parameters defined by OAuth 2.0 and 602 the PoP access token extension, this framework defines parameters 603 that can be used to inform the client about capabilities of the 604 RS, e.g. the profiles the RS supports. More information about 605 these parameters can be found in Section 5.8.4. 607 Resource Request (C): 608 The client interacts with the RS to request access to the 609 protected resource and provides the access token. The protocol to 610 use between the client and the RS is not restricted to CoAP. 611 HTTP, HTTP/2, QUIC, MQTT, Bluetooth Low Energy, etc., are also 612 viable candidates. 614 Depending on the device limitations and the selected protocol, 615 this exchange may be split up into two parts: 617 (1) the client sends the access token containing, or 618 referencing, the authorization information to the RS, that may 619 be used for subsequent resource requests by the client, and 621 (2) the client makes the resource access request, using the 622 communication security protocol and other Access Information 623 obtained from the AS. 625 The Client and the RS mutually authenticate using the security 626 protocol specified in the profile (see step B) and the keys 627 obtained in the access token or the Access Information. The RS 628 verifies that the token is integrity protected and originated by 629 the AS. It then compares the claims contained in the access token 630 with the resource request. If the RS is online, validation can be 631 handed over to the AS using token introspection (see messages D 632 and E) over HTTP or CoAP. 634 Token Introspection Request (D): 635 A resource server may be configured to introspect the access token 636 by including it in a request to the introspection endpoint at that 637 AS. Token introspection over CoAP is defined in Section 5.9 and 638 for HTTP in [RFC7662]. 640 Note that token introspection is an optional step and can be 641 omitted if the token is self-contained and the resource server is 642 prepared to perform the token validation on its own. 644 Token Introspection Response (E): 645 The AS validates the token and returns the most recent parameters, 646 such as scope, audience, validity etc. associated with it back to 647 the RS. The RS then uses the received parameters to process the 648 request to either accept or to deny it. 650 Protected Resource (F): 651 If the request from the client is authorized, the RS fulfills the 652 request and returns a response with the appropriate response code. 653 The RS uses the dynamically established keys to protect the 654 response, according to the communication security protocol used. 656 5. Framework 658 The following sections detail the profiling and extensions of OAuth 659 2.0 for constrained environments, which constitutes the ACE 660 framework. 662 Credential Provisioning 663 For IoT, it cannot be assumed that the client and RS are part of a 664 common key infrastructure, so the AS provisions credentials or 665 associated information to allow mutual authentication between 666 client and RS. The resulting security association between client 667 and RS may then also be used to bind these credentials to the 668 access tokens the client uses. 670 Proof-of-Possession 671 The ACE framework, by default, implements proof-of-possession for 672 access tokens, i.e., that the token holder can prove being a 673 holder of the key bound to the token. The binding is provided by 674 the "cnf" claim [RFC8747] indicating what key is used for proof- 675 of-possession. If a client needs to submit a new access token, 676 e.g., to obtain additional access rights, they can request that 677 the AS binds this token to the same key as the previous one. 679 ACE Profiles 680 The client or RS may be limited in the encodings or protocols it 681 supports. To support a variety of different deployment settings, 682 specific interactions between client and RS are defined in an ACE 683 profile. In ACE framework the AS is expected to manage the 684 matching of compatible profile choices between a client and an RS. 685 The AS informs the client of the selected profile using the 686 "ace_profile" parameter in the token response. 688 OAuth 2.0 requires the use of TLS both to protect the communication 689 between AS and client when requesting an access token; between client 690 and RS when accessing a resource and between AS and RS if 691 introspection is used. In constrained settings TLS is not always 692 feasible, or desirable. Nevertheless it is REQUIRED that the 693 communications named above are encrypted, integrity protected and 694 protected against message replay. It is also REQUIRED that the 695 communicating endpoints perform mutual authentication. Furthermore 696 it MUST be assured that responses are bound to the requests in the 697 sense that the receiver of a response can be certain that the 698 response actually belongs to a certain request. Note that setting up 699 such a secure communication may require some unprotected messages to 700 be exchanged first (e.g. sending the token from the client to the 701 RS). 703 Profiles MUST specify a communication security protocol that provides 704 the features required above. 706 In OAuth 2.0 the communication with the Token and the Introspection 707 endpoints at the AS is assumed to be via HTTP and may use Uri-query 708 parameters. When profiles of this framework use CoAP instead, it is 709 REQUIRED to use of the following alternative instead of Uri-query 710 parameters: The sender (client or RS) encodes the parameters of its 711 request as a CBOR map and submits that map as the payload of the POST 712 request. 714 Profiles that use CBOR encoding of protocol message parameters at the 715 outermost encoding layer MUST use the media format 'application/ 716 ace+cbor'. If CoAP is used for communication, the Content-Format 717 MUST be abbreviated with the ID: 19 (see Section 8.16). 719 The OAuth 2.0 AS uses a JSON structure in the payload of its 720 responses both to client and RS. If CoAP is used, it is REQUIRED to 721 use CBOR [RFC7049] instead of JSON. Depending on the profile, the 722 CBOR payload MAY be enclosed in a non-CBOR cryptographic wrapper. 724 5.1. Discovering Authorization Servers 726 C must discover the AS in charge of RS to determine where to request 727 the access token. To do so, C must 1. find out the AS URI to which 728 the token request message must be sent and 2. MUST validate that the 729 AS with this URI is authorized to provide access tokens for this RS. 731 In order to determine the AS URI, C MAY send an initial Unauthorized 732 Resource Request message to RS. RS then denies the request and sends 733 the address of its AS back to C (see Section 5.2). How C validates 734 the AS authorization is not in scope for this document. C may, e.g., 735 ask it's owner if this AS is authorized for this RS. C may also use 736 a mechanism that addresses both problems at once. 738 5.2. Unauthorized Resource Request Message 740 An Unauthorized Resource Request message is a request for any 741 resource hosted by RS for which the client does not have 742 authorization granted. RSes MUST treat any request for a protected 743 resource as an Unauthorized Resource Request message when any of the 744 following hold: 746 o The request has been received on an unprotected channel. 748 o The RS has no valid access token for the sender of the request 749 regarding the requested action on that resource. 751 o The RS has a valid access token for the sender of the request, but 752 that token does not authorize the requested action on the 753 requested resource. 755 Note: These conditions ensure that the RS can handle requests 756 autonomously once access was granted and a secure channel has been 757 established between C and RS. The authz-info endpoint, as part of 758 the process for authorizing to protected resources, is not itself a 759 protected resource and MUST NOT be protected as specified above (cf. 760 Section 5.10.1). 762 Unauthorized Resource Request messages MUST be denied with an 763 "unauthorized_client" error response. In this response, the Resource 764 Server SHOULD provide proper AS Request Creation Hints to enable the 765 Client to request an access token from RS's AS as described in 766 Section 5.3. 768 The handling of all client requests (including unauthorized ones) by 769 the RS is described in Section 5.10.2. 771 5.3. AS Request Creation Hints 773 The AS Request Creation Hints message is sent by an RS as a response 774 to an Unauthorized Resource Request message (see Section 5.2) to help 775 the sender of the Unauthorized Resource Request message acquire a 776 valid access token. The AS Request Creation Hints message is a CBOR 777 map, with an OPTIONAL element "AS" specifying an absolute URI (see 778 Section 4.3 of [RFC3986]) that identifies the appropriate AS for the 779 RS. 781 The message can also contain the following OPTIONAL parameters: 783 o A "audience" element containing a suggested audience that the 784 client should request at the AS. 786 o A "kid" element containing the key identifier of a key used in an 787 existing security association between the client and the RS. The 788 RS expects the client to request an access token bound to this 789 key, in order to avoid having to re-establish the security 790 association. 792 o A "cnonce" element containing a client-nonce. See Section 5.3.1. 794 o A "scope" element containing the suggested scope that the client 795 should request towards the AS. 797 Figure 2 summarizes the parameters that may be part of the AS Request 798 Creation Hints. 800 /-----------+----------+---------------------\ 801 | Name | CBOR Key | Value Type | 802 |-----------+----------+---------------------| 803 | AS | 1 | text string | 804 | kid | 2 | byte string | 805 | audience | 5 | text string | 806 | scope | 9 | text or byte string | 807 | cnonce | 39 | byte string | 808 \-----------+----------+---------------------/ 810 Figure 2: AS Request Creation Hints 812 Note that the schema part of the AS parameter may need to be adapted 813 to the security protocol that is used between the client and the AS. 814 Thus the example AS value "coap://as.example.com/token" might need to 815 be transformed to "coaps://as.example.com/token". It is assumed that 816 the client can determine the correct schema part on its own depending 817 on the way it communicates with the AS. 819 Figure 3 shows an example for an AS Request Creation Hints message 820 payload using CBOR [RFC7049] diagnostic notation, using the parameter 821 names instead of the CBOR keys for better human readability. 823 4.01 Unauthorized 824 Content-Format: application/ace+cbor 825 Payload : 826 { 827 "AS" : "coaps://as.example.com/token", 828 "audience" : "coaps://rs.example.com" 829 "scope" : "rTempC", 830 "cnonce" : h'e0a156bb3f' 831 } 833 Figure 3: AS Request Creation Hints payload example 835 In the example above, the response parameter "AS" points the receiver 836 of this message to the URI "coaps://as.example.com/token" to request 837 access tokens. The RS sending this response (i.e., RS) uses an 838 internal clock that is only loosely synchronized with the clock of 839 the AS. Therefore it can not reliably verify the expiration time of 840 access tokens it receives. To ensure a certain level of access token 841 freshness nevetheless, the RS has included a "cnonce" parameter (see 842 Section 5.3.1) in the response. 844 Figure 4 illustrates the mandatory to use binary encoding of the 845 message payload shown in Figure 3. 847 a4 # map(4) 848 01 # unsigned(1) (=AS) 849 78 1c # text(28) 850 636f6170733a2f2f61732e657861 851 6d706c652e636f6d2f746f6b656e # "coaps://as.example.com/token" 852 05 # unsigned(5) (=audience) 853 76 # text(22) 854 636f6170733a2f2f72732e657861 855 6d706c652e636f6d # "coaps://rs.example.com" 856 09 # unsigned(9) (=scope) 857 66 # text(6) 858 7254656d7043 # "rTempC" 859 18 27 # unsigned(39) (=cnonce) 860 45 # bytes(5) 861 e0a156bb3f # 863 Figure 4: AS Request Creation Hints example encoded in CBOR 865 5.3.1. The Client-Nonce Parameter 867 If the RS does not synchronize its clock with the AS, it could be 868 tricked into accepting old access tokens, that are either expired or 869 have been compromised. In order to ensure some level of token 870 freshness in that case, the RS can use the "cnonce" (client-nonce) 871 parameter. The processing requirements for this parameter are as 872 follows: 874 o An RS sending a "cnonce" parameter in an AS Request Creation Hints 875 message MUST store information to validate that a given cnonce is 876 fresh. How this is implemented internally is out of scope for 877 this specification. Expiration of client-nonces should be based 878 roughly on the time it would take a client to obtain an access 879 token after receiving the AS Request Creation Hints message, with 880 some allowance for unexpected delays. 882 o A client receiving a "cnonce" parameter in an AS Request Creation 883 Hints message MUST include this in the parameters when requesting 884 an access token at the AS, using the "cnonce" parameter from 885 Section 5.8.4.4. 887 o If an AS grants an access token request containing a "cnonce" 888 parameter, it MUST include this value in the access token, using 889 the "cnonce" claim specified in Section 5.10. 891 o An RS that is using the client-nonce mechanism and that receives 892 an access token MUST verify that this token contains a cnonce 893 claim, with a client-nonce value that is fresh according to the 894 information stored at the first step above. If the cnonce claim 895 is not present or if the cnonce claim value is not fresh, the RS 896 MUST discard the access token. If this was an interaction with 897 the authz-info endpoint the RS MUST also respond with an error 898 message using a response code equivalent to the CoAP code 4.01 899 (Unauthorized). 901 5.4. Authorization Grants 903 To request an access token, the client obtains authorization from the 904 resource owner or uses its client credentials as a grant. The 905 authorization is expressed in the form of an authorization grant. 907 The OAuth framework [RFC6749] defines four grant types. The grant 908 types can be split up into two groups, those granted on behalf of the 909 resource owner (password, authorization code, implicit) and those for 910 the client (client credentials). Further grant types have been added 911 later, such as [RFC7521] defining an assertion-based authorization 912 grant. 914 The grant type is selected depending on the use case. In cases where 915 the client acts on behalf of the resource owner, the authorization 916 code grant is recommended. If the client acts on behalf of the 917 resource owner, but does not have any display or has very limited 918 interaction possibilities, it is recommended to use the device code 919 grant defined in [RFC8628]. In cases where the client acts 920 autonomously the client credentials grant is recommended. 922 For details on the different grant types, see section 1.3 of 923 [RFC6749]. The OAuth 2.0 framework provides an extension mechanism 924 for defining additional grant types, so profiles of this framework 925 MAY define additional grant types, if needed. 927 5.5. Client Credentials 929 Authentication of the client is mandatory independent of the grant 930 type when requesting an access token from the token endpoint. In the 931 case of the client credentials grant type, the authentication and 932 grant coincide. 934 Client registration and provisioning of client credentials to the 935 client is out of scope for this specification. 937 The OAuth framework defines one client credential type in section 938 2.3.1 of [RFC6749]: client id and client secret. 939 [I-D.erdtman-ace-rpcc] adds raw-public-key and pre-shared-key to the 940 client credentials types. Profiles of this framework MAY extend with 941 an additional client credentials type using client certificates. 943 5.6. AS Authentication 945 The client credential grant does not, by default, authenticate the AS 946 that the client connects to. In classic OAuth, the AS is 947 authenticated with a TLS server certificate. 949 Profiles of this framework MUST specify how clients authenticate the 950 AS and how communication security is implemented. By default, server 951 side TLS certificates, as defined by OAuth 2.0, are required. 953 5.7. The Authorization Endpoint 955 The OAuth 2.0 authorization endpoint is used to interact with the 956 resource owner and obtain an authorization grant, in certain grant 957 flows. The primary use case for the ACE-OAuth framework is for 958 machine-to-machine interactions that do not involve the resource 959 owner in the authorization flow; therefore, this endpoint is out of 960 scope here. Future profiles may define constrained adaptation 961 mechanisms for this endpoint as well. Non-constrained clients 962 interacting with constrained resource servers can use the 963 specification in section 3.1 of [RFC6749] and the attack 964 countermeasures suggested in section 4.2 of [RFC6819]. 966 5.8. The Token Endpoint 968 In standard OAuth 2.0, the AS provides the token endpoint for 969 submitting access token requests. This framework extends the 970 functionality of the token endpoint, giving the AS the possibility to 971 help the client and RS to establish shared keys or to exchange their 972 public keys. Furthermore, this framework defines encodings using 973 CBOR, as a substitute for JSON. 975 The endpoint may, however, be exposed over HTTPS as in classical 976 OAuth or even other transports. A profile MUST define the details of 977 the mapping between the fields described below, and these transports. 978 If HTTPS is used, JSON or CBOR payloads may be supported. If JSON 979 payloads are used, the semantics of Section 4 of the OAuth 2.0 980 specification MUST be followed (with additions as described below). 981 If CBOR payload is supported, the semantics described below MUST be 982 followed. 984 For the AS to be able to issue a token, the client MUST be 985 authenticated and present a valid grant for the scopes requested. 986 Profiles of this framework MUST specify how the AS authenticates the 987 client and how the communication between client and AS is protected, 988 fulfilling the requirements specified in Section 5. 990 The default name of this endpoint in an url-path is '/token', however 991 implementations are not required to use this name and can define 992 their own instead. 994 The figures of this section use CBOR diagnostic notation without the 995 integer abbreviations for the parameters or their values for 996 illustrative purposes. Note that implementations MUST use the 997 integer abbreviations and the binary CBOR encoding, if the CBOR 998 encoding is used. 1000 5.8.1. Client-to-AS Request 1002 The client sends a POST request to the token endpoint at the AS. The 1003 profile MUST specify how the communication is protected. The content 1004 of the request consists of the parameters specified in the relevant 1005 subsection of section 4 of the OAuth 2.0 specification [RFC6749], 1006 depending on the grant type, with the following exceptions and 1007 additions: 1009 o The parameter "grant_type" is OPTIONAL in the context of this 1010 framework (as opposed to REQUIRED in RFC6749). If that parameter 1011 is missing, the default value "client_credentials" is implied. 1013 o The "audience" parameter from [RFC8693] is OPTIONAL to request an 1014 access token bound to a specific audience. 1016 o The "cnonce" parameter defined in Section 5.8.4.4 is REQUIRED if 1017 the RS provided a client-nonce in the "AS Request Creation Hints" 1018 message Section 5.3 1020 o The "scope" parameter MAY be encoded as a byte string instead of 1021 the string encoding specified in section 3.3 of [RFC6749], in 1022 order allow compact encoding of complex scopes. The syntax of 1023 such a binary encoding is explicitly not specified here and left 1024 to profiles or applications, specifically note that a binary 1025 encoded scope does not necessarily use the space character '0x20' 1026 to delimit scope-tokens. 1028 o The client can send an empty (null value) "ace_profile" parameter 1029 to indicate that it wants the AS to include the "ace_profile" 1030 parameter in the response. See Section 5.8.4.3. 1032 o A client MUST be able to use the parameters from 1033 [I-D.ietf-ace-oauth-params] in an access token request to the 1034 token endpoint and the AS MUST be able to process these additional 1035 parameters. 1037 The default behavior, is that the AS generates a symmetric proof-of- 1038 possession key for the client. In order to use an asymmetric key 1039 pair or to re-use a key previously established with the RS, the 1040 client is supposed to use the "req_cnf" parameter from 1041 [I-D.ietf-ace-oauth-params]. 1043 If CBOR is used then these parameters MUST be provided as a CBOR map. 1045 When HTTP is used as a transport then the client makes a request to 1046 the token endpoint by sending the parameters using the "application/ 1047 x-www-form-urlencoded" format with a character encoding of UTF-8 in 1048 the HTTP request entity-body, as defined in section 3.2 of [RFC6749]. 1050 The following examples illustrate different types of requests for 1051 proof-of-possession tokens. 1053 Figure 5 shows a request for a token with a symmetric proof-of- 1054 possession key. The content is displayed in CBOR diagnostic 1055 notation, without abbreviations for better readability. 1057 Header: POST (Code=0.02) 1058 Uri-Host: "as.example.com" 1059 Uri-Path: "token" 1060 Content-Format: "application/ace+cbor" 1061 Payload: 1062 { 1063 "client_id" : "myclient", 1064 "audience" : "tempSensor4711" 1065 } 1067 Figure 5: Example request for an access token bound to a symmetric 1068 key. 1070 Figure 6 shows a request for a token with an asymmetric proof-of- 1071 possession key. Note that in this example OSCORE [RFC8613] is used 1072 to provide object-security, therefore the Content-Format is 1073 "application/oscore" wrapping the "application/ace+cbor" type 1074 content. The OSCORE option has a decoded interpretation appended in 1075 parentheses for the reader's convenience. Also note that in this 1076 example the audience is implicitly known by both client and AS. 1077 Furthermore note that this example uses the "req_cnf" parameter from 1078 [I-D.ietf-ace-oauth-params]. 1080 Header: POST (Code=0.02) 1081 Uri-Host: "as.example.com" 1082 Uri-Path: "token" 1083 OSCORE: 0x09, 0x05, 0x44, 0x6C 1084 (h=0, k=1, n=001, partialIV= 0x05, kid=[0x44, 0x6C]) 1085 Content-Format: "application/oscore" 1086 Payload: 1087 0x44025d1 ... (full payload omitted for brevity) ... 68b3825e 1089 Decrypted payload: 1090 { 1091 "client_id" : "myclient", 1092 "req_cnf" : { 1093 "COSE_Key" : { 1094 "kty" : "EC", 1095 "kid" : h'11', 1096 "crv" : "P-256", 1097 "x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8', 1098 "y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4' 1099 } 1100 } 1101 } 1103 Figure 6: Example token request bound to an asymmetric key. 1105 Figure 7 shows a request for a token where a previously communicated 1106 proof-of-possession key is only referenced using the "req_cnf" 1107 parameter from [I-D.ietf-ace-oauth-params]. 1109 Header: POST (Code=0.02) 1110 Uri-Host: "as.example.com" 1111 Uri-Path: "token" 1112 Content-Format: "application/ace+cbor" 1113 Payload: 1114 { 1115 "client_id" : "myclient", 1116 "audience" : "valve424", 1117 "scope" : "read", 1118 "req_cnf" : { 1119 "kid" : b64'6kg0dXJM13U' 1120 } 1121 }W 1123 Figure 7: Example request for an access token bound to a key 1124 reference. 1126 Refresh tokens are typically not stored as securely as proof-of- 1127 possession keys in requesting clients. Proof-of-possession based 1128 refresh token requests MUST NOT request different proof-of-possession 1129 keys or different audiences in token requests. Refresh token 1130 requests can only use to request access tokens bound to the same 1131 proof-of-possession key and the same audience as access tokens issued 1132 in the initial token request. 1134 5.8.2. AS-to-Client Response 1136 If the access token request has been successfully verified by the AS 1137 and the client is authorized to obtain an access token corresponding 1138 to its access token request, the AS sends a response with the 1139 response code equivalent to the CoAP response code 2.01 (Created). 1140 If client request was invalid, or not authorized, the AS returns an 1141 error response as described in Section 5.8.3. 1143 Note that the AS decides which token type and profile to use when 1144 issuing a successful response. It is assumed that the AS has prior 1145 knowledge of the capabilities of the client and the RS (see 1146 Appendix D). This prior knowledge may, for example, be set by the 1147 use of a dynamic client registration protocol exchange [RFC7591]. If 1148 the client has requested a specific proof-of-possession key using the 1149 "req_cnf" parameter from [I-D.ietf-ace-oauth-params], this may also 1150 influence which profile the AS selects, as it needs to support the 1151 use of the key type requested the client. 1153 The content of the successful reply is the Access Information. When 1154 using CBOR payloads, the content MUST be encoded as a CBOR map, 1155 containing parameters as specified in Section 5.1 of [RFC6749], with 1156 the following additions and changes: 1158 ace_profile: 1159 OPTIONAL unless the request included an empty ace_profile 1160 parameter in which case it is MANDATORY. This indicates the 1161 profile that the client MUST use towards the RS. See 1162 Section 5.8.4.3 for the formatting of this parameter. If this 1163 parameter is absent, the AS assumes that the client implicitly 1164 knows which profile to use towards the RS. 1166 token_type: 1167 This parameter is OPTIONAL, as opposed to 'required' in [RFC6749]. 1168 By default implementations of this framework SHOULD assume that 1169 the token_type is "PoP". If a specific use case requires another 1170 token_type (e.g., "Bearer") to be used then this parameter is 1171 REQUIRED. 1173 Furthermore [I-D.ietf-ace-oauth-params] defines additional parameters 1174 that the AS MUST be able to use when responding to a request to the 1175 token endpoint. 1177 Figure 8 summarizes the parameters that can currently be part of the 1178 Access Information. Future extensions may define additional 1179 parameters. 1181 /-------------------+-------------------------------\ 1182 | Parameter name | Specified in | 1183 |-------------------+-------------------------------| 1184 | access_token | RFC 6749 | 1185 | token_type | RFC 6749 | 1186 | expires_in | RFC 6749 | 1187 | refresh_token | RFC 6749 | 1188 | scope | RFC 6749 | 1189 | state | RFC 6749 | 1190 | error | RFC 6749 | 1191 | error_description | RFC 6749 | 1192 | error_uri | RFC 6749 | 1193 | ace_profile | [this document] | 1194 | cnf | [I-D.ietf-ace-oauth-params] | 1195 | rs_cnf | [I-D.ietf-ace-oauth-params] | 1196 \-------------------+-------------------------------/ 1198 Figure 8: Access Information parameters 1200 Figure 9 shows a response containing a token and a "cnf" parameter 1201 with a symmetric proof-of-possession key, which is defined in 1202 [I-D.ietf-ace-oauth-params]. Note that the key identifier 'kid' is 1203 only used to simplify indexing and retrieving the key, and no 1204 assumptions should be made that it is unique in the domains of either 1205 the client or the RS. 1207 Header: Created (Code=2.01) 1208 Content-Format: "application/ace+cbor" 1209 Payload: 1210 { 1211 "access_token" : b64'SlAV32hkKG ... 1212 (remainder of CWT omitted for brevity; 1213 CWT contains COSE_Key in the "cnf" claim)', 1214 "ace_profile" : "coap_dtls", 1215 "expires_in" : "3600", 1216 "cnf" : { 1217 "COSE_Key" : { 1218 "kty" : "Symmetric", 1219 "kid" : b64'39Gqlw', 1220 "k" : b64'hJtXhkV8FJG+Onbc6mxCcQh' 1221 } 1222 } 1223 } 1225 Figure 9: Example AS response with an access token bound to a 1226 symmetric key. 1228 5.8.3. Error Response 1230 The error responses for CoAP-based interactions with the AS are 1231 generally equivalent to the ones for HTTP-based interactions as 1232 defined in Section 5.2 of [RFC6749], with the following exceptions: 1234 o When using CBOR the raw payload before being processed by the 1235 communication security protocol MUST be encoded as a CBOR map. 1237 o A response code equivalent to the CoAP code 4.00 (Bad Request) 1238 MUST be used for all error responses, except for invalid_client 1239 where a response code equivalent to the CoAP code 4.01 1240 (Unauthorized) MAY be used under the same conditions as specified 1241 in Section 5.2 of [RFC6749]. 1243 o The Content-Format (for CoAP-based interactions) or media type 1244 (for HTTP-based interactions) "application/ace+cbor" MUST be used 1245 for the error response. 1247 o The parameters "error", "error_description" and "error_uri" MUST 1248 be abbreviated using the codes specified in Figure 12, when a CBOR 1249 encoding is used. 1251 o The error code (i.e., value of the "error" parameter) MUST be 1252 abbreviated as specified in Figure 10, when a CBOR encoding is 1253 used. 1255 /---------------------------+-------------\ 1256 | Name | CBOR Values | 1257 |---------------------------+-------------| 1258 | invalid_request | 1 | 1259 | invalid_client | 2 | 1260 | invalid_grant | 3 | 1261 | unauthorized_client | 4 | 1262 | unsupported_grant_type | 5 | 1263 | invalid_scope | 6 | 1264 | unsupported_pop_key | 7 | 1265 | incompatible_ace_profiles | 8 | 1266 \---------------------------+-------------/ 1268 Figure 10: CBOR abbreviations for common error codes 1270 In addition to the error responses defined in OAuth 2.0, the 1271 following behavior MUST be implemented by the AS: 1273 o If the client submits an asymmetric key in the token request that 1274 the RS cannot process, the AS MUST reject that request with a 1275 response code equivalent to the CoAP code 4.00 (Bad Request) 1276 including the error code "unsupported_pop_key" defined in 1277 Figure 10. 1279 o If the client and the RS it has requested an access token for do 1280 not share a common profile, the AS MUST reject that request with a 1281 response code equivalent to the CoAP code 4.00 (Bad Request) 1282 including the error code "incompatible_ace_profiles" defined in 1283 Figure 10. 1285 5.8.4. Request and Response Parameters 1287 This section provides more detail about the new parameters that can 1288 be used in access token requests and responses, as well as 1289 abbreviations for more compact encoding of existing parameters and 1290 common parameter values. 1292 5.8.4.1. Grant Type 1294 The abbreviations specified in the registry defined in Section 8.5 1295 MUST be used in CBOR encodings instead of the string values defined 1296 in [RFC6749], if CBOR payloads are used. 1298 /--------------------+------------+------------------------\ 1299 | Name | CBOR Value | Original Specification | 1300 |--------------------+------------+------------------------| 1301 | password | 0 | [RFC6749] | 1302 | authorization_code | 1 | [RFC6749] | 1303 | client_credentials | 2 | [RFC6749] | 1304 | refresh_token | 3 | [RFC6749] | 1305 \--------------------+------------+------------------------/ 1307 Figure 11: CBOR abbreviations for common grant types 1309 5.8.4.2. Token Type 1311 The "token_type" parameter, defined in section 5.1 of [RFC6749], 1312 allows the AS to indicate to the client which type of access token it 1313 is receiving (e.g., a bearer token). 1315 This document registers the new value "PoP" for the OAuth Access 1316 Token Types registry, specifying a proof-of-possession token. How 1317 the proof-of-possession by the client to the RS is performed MUST be 1318 specified by the profiles. 1320 The values in the "token_type" parameter MUST use the CBOR 1321 abbreviations defined in the registry specified by Section 8.7, if a 1322 CBOR encoding is used. 1324 In this framework the "pop" value for the "token_type" parameter is 1325 the default. The AS may, however, provide a different value. 1327 5.8.4.3. Profile 1329 Profiles of this framework MUST define the communication protocol and 1330 the communication security protocol between the client and the RS. 1331 The security protocol MUST provide encryption, integrity and replay 1332 protection. It MUST also provide a binding between requests and 1333 responses. Furthermore profiles MUST define a list of allowed proof- 1334 of-possession methods, if they support proof-of-possession tokens. 1336 A profile MUST specify an identifier that MUST be used to uniquely 1337 identify itself in the "ace_profile" parameter. The textual 1338 representation of the profile identifier is intended for human 1339 readability and for JSON-based interactions, it MUST NOT be used for 1340 CBOR-based interactions. Profiles MUST register their identifier in 1341 the registry defined in Section 8.8. 1343 Profiles MAY define additional parameters for both the token request 1344 and the Access Information in the access token response in order to 1345 support negotiation or signaling of profile specific parameters. 1347 Clients that want the AS to provide them with the "ace_profile" 1348 parameter in the access token response can indicate that by sending a 1349 ace_profile parameter with a null value (for CBOR-based interactions) 1350 or an empty string (for JSON based interactions) in the access token 1351 request. 1353 5.8.4.4. Client-Nonce 1355 This parameter MUST be sent from the client to the AS, if it 1356 previously received a "cnonce" parameter in the AS Request Creation 1357 Hints Section 5.3. The parameter is encoded as a byte string for 1358 CBOR-based interactions, and as a string (Base64 encoded binary) for 1359 JSON-based interactions. It MUST copy the value from the cnonce 1360 parameter in the AS Request Creation Hints. 1362 5.8.5. Mapping Parameters to CBOR 1364 If CBOR encoding is used, all OAuth parameters in access token 1365 requests and responses MUST be mapped to CBOR types as specified in 1366 the registry defined by Section 8.10, using the given integer 1367 abbreviation for the map keys. 1369 Note that we have aligned the abbreviations corresponding to claims 1370 with the abbreviations defined in [RFC8392]. 1372 Note also that abbreviations from -24 to 23 have a 1 byte encoding 1373 size in CBOR. We have thus chosen to assign abbreviations in that 1374 range to parameters we expect to be used most frequently in 1375 constrained scenarios. 1377 /-------------------+----------+---------------------\ 1378 | Name | CBOR Key | Value Type | 1379 |-------------------+----------+---------------------| 1380 | access_token | 1 | byte string | 1381 | expires_in | 2 | unsigned integer | 1382 | audience | 5 | text string | 1383 | scope | 9 | text or byte string | 1384 | client_id | 24 | text string | 1385 | client_secret | 25 | byte string | 1386 | response_type | 26 | text string | 1387 | redirect_uri | 27 | text string | 1388 | state | 28 | text string | 1389 | code | 29 | byte string | 1390 | error | 30 | integer | 1391 | error_description | 31 | text string | 1392 | error_uri | 32 | text string | 1393 | grant_type | 33 | unsigned integer | 1394 | token_type | 34 | integer | 1395 | username | 35 | text string | 1396 | password | 36 | text string | 1397 | refresh_token | 37 | byte string | 1398 | ace_profile | 38 | integer | 1399 | cnonce | 39 | byte string | 1400 \-------------------+----------+---------------------/ 1402 Figure 12: CBOR mappings used in token requests and responses 1404 5.9. The Introspection Endpoint 1406 Token introspection [RFC7662] can be OPTIONALLY provided by the AS, 1407 and is then used by the RS and potentially the client to query the AS 1408 for metadata about a given token, e.g., validity or scope. Analogous 1409 to the protocol defined in [RFC7662] for HTTP and JSON, this section 1410 defines adaptations to more constrained environments using CBOR and 1411 leaving the choice of the application protocol to the profile. 1413 Communication between the requesting entity and the introspection 1414 endpoint at the AS MUST be integrity protected and encrypted. The 1415 communication security protocol MUST also provide a binding between 1416 requests and responses. Furthermore the two interacting parties MUST 1417 perform mutual authentication. Finally the AS SHOULD verify that the 1418 requesting entity has the right to access introspection information 1419 about the provided token. Profiles of this framework that support 1420 introspection MUST specify how authentication and communication 1421 security between the requesting entity and the AS is implemented. 1423 The default name of this endpoint in an url-path is '/introspect', 1424 however implementations are not required to use this name and can 1425 define their own instead. 1427 The figures of this section uses CBOR diagnostic notation without the 1428 integer abbreviations for the parameters or their values for better 1429 readability. 1431 Note that supporting introspection is OPTIONAL for implementations of 1432 this framework. 1434 5.9.1. Introspection Request 1436 The requesting entity sends a POST request to the introspection 1437 endpoint at the AS. The profile MUST specify how the communication 1438 is protected. If CBOR is used, the payload MUST be encoded as a CBOR 1439 map with a "token" entry containing the access token. Further 1440 optional parameters representing additional context that is known by 1441 the requesting entity to aid the AS in its response MAY be included. 1443 For CoAP-based interaction, all messages MUST use the content type 1444 "application/ace+cbor", while for HTTP-based interactions the 1445 equivalent media type "application/ace+cbor" MUST be used. 1447 The same parameters are required and optional as in Section 2.1 of 1448 [RFC7662]. 1450 For example, Figure 13 shows an RS calling the token introspection 1451 endpoint at the AS to query about an OAuth 2.0 proof-of-possession 1452 token. Note that object security based on OSCORE [RFC8613] is 1453 assumed in this example, therefore the Content-Format is 1454 "application/oscore". Figure 14 shows the decoded payload. 1456 Header: POST (Code=0.02) 1457 Uri-Host: "as.example.com" 1458 Uri-Path: "introspect" 1459 OSCORE: 0x09, 0x05, 0x25 1460 Content-Format: "application/oscore" 1461 Payload: 1462 ... COSE content ... 1464 Figure 13: Example introspection request. 1466 { 1467 "token" : b64'7gj0dXJQ43U', 1468 "token_type_hint" : "PoP" 1469 } 1471 Figure 14: Decoded payload. 1473 5.9.2. Introspection Response 1475 If the introspection request is authorized and successfully 1476 processed, the AS sends a response with the response code equivalent 1477 to the CoAP code 2.01 (Created). If the introspection request was 1478 invalid, not authorized or couldn't be processed the AS returns an 1479 error response as described in Section 5.9.3. 1481 In a successful response, the AS encodes the response parameters in a 1482 map including with the same required and optional parameters as in 1483 Section 2.2 of [RFC7662] with the following addition: 1485 ace_profile OPTIONAL. This indicates the profile that the RS MUST 1486 use with the client. See Section 5.8.4.3 for more details on the 1487 formatting of this parameter. 1489 cnonce OPTIONAL. A client-nonce provided to the AS by the client. 1490 The RS MUST verify that this corresponds to the client-nonce 1491 previously provided to the client in the AS Request Creation 1492 Hints. See Section 5.3 and Section 5.8.4.4. 1494 exi OPTIONAL. The "expires-in" claim associated to this access 1495 token. See Section 5.10.3. 1497 Furthermore [I-D.ietf-ace-oauth-params] defines more parameters that 1498 the AS MUST be able to use when responding to a request to the 1499 introspection endpoint. 1501 For example, Figure 15 shows an AS response to the introspection 1502 request in Figure 13. Note that this example contains the "cnf" 1503 parameter defined in [I-D.ietf-ace-oauth-params]. 1505 Header: Created (Code=2.01) 1506 Content-Format: "application/ace+cbor" 1507 Payload: 1508 { 1509 "active" : true, 1510 "scope" : "read", 1511 "ace_profile" : "coap_dtls", 1512 "cnf" : { 1513 "COSE_Key" : { 1514 "kty" : "Symmetric", 1515 "kid" : b64'39Gqlw', 1516 "k" : b64'hJtXhkV8FJG+Onbc6mxCcQh' 1517 } 1518 } 1519 } 1521 Figure 15: Example introspection response. 1523 5.9.3. Error Response 1525 The error responses for CoAP-based interactions with the AS are 1526 equivalent to the ones for HTTP-based interactions as defined in 1527 Section 2.3 of [RFC7662], with the following differences: 1529 o If content is sent and CBOR is used the payload MUST be encoded as 1530 a CBOR map and the Content-Format "application/ace+cbor" MUST be 1531 used. 1533 o If the credentials used by the requesting entity (usually the RS) 1534 are invalid the AS MUST respond with the response code equivalent 1535 to the CoAP code 4.01 (Unauthorized) and use the required and 1536 optional parameters from Section 5.2 in [RFC6749]. 1538 o If the requesting entity does not have the right to perform this 1539 introspection request, the AS MUST respond with a response code 1540 equivalent to the CoAP code 4.03 (Forbidden). In this case no 1541 payload is returned. 1543 o The parameters "error", "error_description" and "error_uri" MUST 1544 be abbreviated using the codes specified in Figure 12. 1546 o The error codes MUST be abbreviated using the codes specified in 1547 the registry defined by Section 8.4. 1549 Note that a properly formed and authorized query for an inactive or 1550 otherwise invalid token does not warrant an error response by this 1551 specification. In these cases, the authorization server MUST instead 1552 respond with an introspection response with the "active" field set to 1553 "false". 1555 5.9.4. Mapping Introspection parameters to CBOR 1557 If CBOR is used, the introspection request and response parameters 1558 MUST be mapped to CBOR types as specified in the registry defined by 1559 Section 8.12, using the given integer abbreviation for the map key. 1561 Note that we have aligned abbreviations that correspond to a claim 1562 with the abbreviations defined in [RFC8392] and the abbreviations of 1563 parameters with the same name from Section 5.8.5. 1565 /-------------------+----------+-------------------------\ 1566 | Parameter name | CBOR Key | Value Type | 1567 |-------------------+----------+-------------------------| 1568 | iss | 1 | text string | 1569 | sub | 2 | text string | 1570 | aud | 3 | text string | 1571 | exp | 4 | integer or | 1572 | | | floating-point number | 1573 | nbf | 5 | integer or | 1574 | | | floating-point number | 1575 | iat | 6 | integer or | 1576 | | | floating-point number | 1577 | cti | 7 | byte string | 1578 | scope | 9 | text or byte string | 1579 | active | 10 | True or False | 1580 | token | 11 | byte string | 1581 | client_id | 24 | text string | 1582 | error | 30 | integer | 1583 | error_description | 31 | text string | 1584 | error_uri | 32 | text string | 1585 | token_type_hint | 33 | text string | 1586 | token_type | 34 | integer | 1587 | username | 35 | text string | 1588 | ace_profile | 38 | integer | 1589 | cnonce | 39 | byte string | 1590 | exi | 40 | unsigned integer | 1591 \-------------------+----------+-------------------------/ 1593 Figure 16: CBOR Mappings to Token Introspection Parameters. 1595 5.10. The Access Token 1597 This framework RECOMMENDS the use of CBOR web token (CWT) as 1598 specified in [RFC8392]. 1600 In order to facilitate offline processing of access tokens, this 1601 document uses the "cnf" claim from [RFC8747] and the "scope" claim 1602 from [RFC8693] for JWT- and CWT-encoded tokens. In addition to 1603 string encoding specified for the "scope" claim, a binary encoding 1604 MAY be used. The syntax of such an encoding is explicitly not 1605 specified here and left to profiles or applications, specifically 1606 note that a binary encoded scope does not necessarily use the space 1607 character '0x20' to delimit scope-tokens. 1609 If the AS needs to convey a hint to the RS about which profile it 1610 should use to communicate with the client, the AS MAY include an 1611 "ace_profile" claim in the access token, with the same syntax and 1612 semantics as defined in Section 5.8.4.3. 1614 If the client submitted a client-nonce parameter in the access token 1615 request Section 5.8.4.4, the AS MUST include the value of this 1616 parameter in the "cnonce" claim specified here. The "cnonce" claim 1617 uses binary encoding. 1619 5.10.1. The Authorization Information Endpoint 1621 The access token, containing authorization information and 1622 information about the proof-of-possession method used by the client, 1623 needs to be transported to the RS so that the RS can authenticate and 1624 authorize the client request. 1626 This section defines a method for transporting the access token to 1627 the RS using a RESTful protocol such as CoAP. Profiles of this 1628 framework MAY define other methods for token transport. 1630 The method consists of an authz-info endpoint, implemented by the RS. 1631 A client using this method MUST make a POST request to the authz-info 1632 endpoint at the RS with the access token in the payload. The RS 1633 receiving the token MUST verify the validity of the token. If the 1634 token is valid, the RS MUST respond to the POST request with 2.01 1635 (Created). Section Section 5.10.1.1 outlines how an RS MUST proceed 1636 to verify the validity of an access token. 1638 The RS MUST be prepared to store at least one access token for future 1639 use. This is a difference to how access tokens are handled in OAuth 1640 2.0, where the access token is typically sent along with each 1641 request, and therefore not stored at the RS. 1643 This specification RECOMMENDS that an RS stores only one token per 1644 proof-of-possession key, meaning that an additional token linked to 1645 the same key will overwrite any existing token at the RS. The reason 1646 is that this greatly simplifies (constrained) implementations, with 1647 respect to required storage and resolving a request to the applicable 1648 token. 1650 If the payload sent to the authz-info endpoint does not parse to a 1651 token, the RS MUST respond with a response code equivalent to the 1652 CoAP code 4.00 (Bad Request). 1654 The RS MAY make an introspection request to validate the token before 1655 responding to the POST request to the authz-info endpoint, e.g. if 1656 the token is an opaque reference. Some transport protocols may 1657 provide a way to indicate that the RS is busy and the client should 1658 retry after an interval; this type of status update would be 1659 appropriate while the RS is waiting for an introspection response. 1661 Profiles MUST specify whether the authz-info endpoint is protected, 1662 including whether error responses from this endpoint are protected. 1663 Note that since the token contains information that allow the client 1664 and the RS to establish a security context in the first place, mutual 1665 authentication may not be possible at this point. 1667 The default name of this endpoint in an url-path is '/authz-info', 1668 however implementations are not required to use this name and can 1669 define their own instead. 1671 5.10.1.1. Verifying an Access Token 1673 When an RS receives an access token, it MUST verify it before storing 1674 it. The details of token verification depends on various aspects, 1675 including the token encoding, the type of token, the security 1676 protection applied to the token, and the claims. The token encoding 1677 matters since the security wrapper differs between the token 1678 encodings. For example, a CWT token uses COSE while a JWT token uses 1679 JOSE. The type of token also has an influence on the verification 1680 procedure since tokens may be self-contained whereby token 1681 verification may happen locally at the RS while a token-by-reference 1682 requires further interaction with the authorization server, for 1683 example using token introspection, to obtain the claims associated 1684 with the token reference. Self-contained tokens MUST, at a minimum, 1685 be integrity protected but they MAY also be encrypted. 1687 For self-contained tokens the RS MUST process the security protection 1688 of the token first, as specified by the respective token format. For 1689 CWT the description can be found in [RFC8392] and for JWT the 1690 relevant specification is [RFC7519]. This MUST include a 1691 verification that security protection (and thus the token) was 1692 generated by an AS that has the right to issue access tokens for this 1693 RS. 1695 In case the token is communicated by reference the RS needs to obtain 1696 the claims first. When the RS uses token introspection the relevant 1697 specification is [RFC7662] with CoAP transport specified in 1698 Section 5.9. 1700 Errors may happen during this initial processing stage: 1702 o If token or claim verification fails, the RS MUST discard the 1703 token and, if this was an interaction with authz-info, return an 1704 error message with a response code equivalent to the CoAP code 1705 4.01 (Unauthorized). 1707 o If the claims cannot be obtained the RS MUST discard the token 1708 and, in case of an interaction via the authz-info endpoint, return 1709 an error message with a response code equivalent to the CoAP code 1710 4.00 (Bad Request). 1712 Next, the RS MUST verify claims, if present, contained in the access 1713 token. Errors are returned when claim checks fail, in the order of 1714 priority of this list: 1716 iss The issuer claim must identify an AS that has the authority to 1717 issue access tokens for the receiving RS. If that is not the case 1718 the RS MUST discard the token. If this was an interaction with 1719 authz-info, the RS MUST also respond with a response code 1720 equivalent to the CoAP code 4.01 (Unauthorized). 1722 exp The expiration date must be in the future. If that is not the 1723 case the RS MUST discard the token. If this was an interaction 1724 with authz-info the RS MUST also respond with a response code 1725 equivalent to the CoAP code 4.01 (Unauthorized). Note that the RS 1726 has to terminate access rights to the protected resources at the 1727 time when the tokens expire. 1729 aud The audience claim must refer to an audience that the RS 1730 identifies with. If that is not the case the RS MUST discard the 1731 token. If this was an interaction with authz-info, the RS MUST 1732 also respond with a response code equivalent to the CoAP code 4.03 1733 (Forbidden). 1735 scope The RS must recognize value of the scope claim. If that is 1736 not the case the RS MUST discard the token. If this was an 1737 interaction with authz-info, the RS MUST also respond with a 1738 response code equivalent to the CoAP code 4.00 (Bad Request). The 1739 RS MAY provide additional information in the error response, to 1740 clarify what went wrong. 1742 Additional processing may be needed for other claims in a way 1743 specific to a profile or the underlying application. 1745 Note that the Subject (sub) claim cannot always be verified when the 1746 token is submitted to the RS since the client may not have 1747 authenticated yet. Also note that a counter for the expires_in (exi) 1748 claim MUST be initialized when the RS first verifies this token. 1750 Also note that profiles of this framework may define access token 1751 transport mechanisms that do not allow for error responses. 1752 Therefore the error messages specified here only apply if the token 1753 was sent to the authz-info endpoint. 1755 When sending error responses, the RS MAY use the error codes from 1756 Section 3.1 of [RFC6750], to provide additional details to the 1757 client. 1759 5.10.1.2. Protecting the Authorization Information Endpoint 1761 As this framework can be used in RESTful environments, it is 1762 important to make sure that attackers cannot perform unauthorized 1763 requests on the authz-info endpoints, other than submitting access 1764 tokens. 1766 Specifically it SHOULD NOT be possible to perform GET, DELETE or PUT 1767 on the authz-info endpoint and on it's children (if any). 1769 The POST method SHOULD NOT be allowed on children of the authz-info 1770 endpoint. 1772 The RS SHOULD implement rate limiting measures to mitigate attacks 1773 aiming to overload the processing capacity of the RS by repeatedly 1774 submitting tokens. For CoAP-based communication the RS could use the 1775 mechanisms from [RFC8516] to indicate that it is overloaded. 1777 5.10.2. Client Requests to the RS 1779 Before sending a request to an RS, the client MUST verify that the 1780 keys used to protect this communication are still valid. See 1781 Section 5.10.4 for details on how the client determines the validity 1782 of the keys used. 1784 If an RS receives a request from a client, and the target resource 1785 requires authorization, the RS MUST first verify that it has an 1786 access token that authorizes this request, and that the client has 1787 performed the proof-of-possession binding that token to the request. 1789 The response code MUST be 4.01 (Unauthorized) in case the client has 1790 not performed the proof-of-possession, or if RS has no valid access 1791 token for the client. If RS has an access token for the client but 1792 the token does not authorize access for the resource that was 1793 requested, RS MUST reject the request with a 4.03 (Forbidden). If RS 1794 has an access token for the client but it does not cover the action 1795 that was requested on the resource, RS MUST reject the request with a 1796 4.05 (Method Not Allowed). 1798 Note: The use of the response codes 4.03 and 4.05 is intended to 1799 prevent infinite loops where a dumb Client optimistically tries to 1800 access a requested resource with any access token received from AS. 1801 As malicious clients could pretend to be C to determine C's 1802 privileges, these detailed response codes must be used only when a 1803 certain level of security is already available which can be achieved 1804 only when the Client is authenticated. 1806 Note: The RS MAY use introspection for timely validation of an access 1807 token, at the time when a request is presented. 1809 Note: Matching the claims of the access token (e.g., scope) to a 1810 specific request is application specific. 1812 If the request matches a valid token and the client has performed the 1813 proof-of-possession for that token, the RS continues to process the 1814 request as specified by the underlying application. 1816 5.10.3. Token Expiration 1818 Depending on the capabilities of the RS, there are various ways in 1819 which it can verify the expiration of a received access token. Here 1820 follows a list of the possibilities including what functionality they 1821 require of the RS. 1823 o The token is a CWT and includes an "exp" claim and possibly the 1824 "nbf" claim. The RS verifies these by comparing them to values 1825 from its internal clock as defined in [RFC7519]. In this case the 1826 RS's internal clock must reflect the current date and time, or at 1827 least be synchronized with the AS's clock. How this clock 1828 synchronization would be performed is out of scope for this 1829 specification. 1831 o The RS verifies the validity of the token by performing an 1832 introspection request as specified in Section 5.9. This requires 1833 the RS to have a reliable network connection to the AS and to be 1834 able to handle two secure sessions in parallel (C to RS and RS to 1835 AS). 1837 o In order to support token expiration for devices that have no 1838 reliable way of synchronizing their internal clocks, this 1839 specification defines the following approach: The claim "exi" 1840 ("expires in") can be used, to provide the RS with the lifetime of 1841 the token in seconds from the time the RS first receives the 1842 token. For CBOR-based interaction this parameter is encoded as 1843 unsigned integer, while JSON-based interactions encode this as 1844 JSON number. 1846 o Processing this claim requires that the RS does the following: 1848 * For each token the RS receives, that contains an "exi" claim: 1849 Keep track of the time it received that token and revisit that 1850 list regularly to expunge expired tokens. 1852 * Keep track of the identifiers of tokens containing the "exi" 1853 claim that have expired (in order to avoid accepting them 1854 again). In order to avoid an unbounded memory usage growth, 1855 this MUST be implemented in the following way when the "exi" 1856 claim is used: 1858 + When creating the token, the AS MUST add a 'cti' claim ( or 1859 'jti' for JWTs) to the access token. The value of this 1860 claim MUST be created as the binary representation of the 1861 concatenation of the identifier of the RS with a sequence 1862 number counting the tokens containing an 'exi' claim, issued 1863 by this AS for the RS. 1865 + The RS MUST store the highest sequence number of an expired 1866 token containing the "exi" claim that it has seen, and treat 1867 tokens with lower sequence numbers as expired. 1869 If a token that authorizes a long running request such as a CoAP 1870 Observe [RFC7641] expires, the RS MUST send an error response with 1871 the response code equivalent to the CoAP code 4.01 (Unauthorized) to 1872 the client and then terminate processing the long running request. 1874 5.10.4. Key Expiration 1876 The AS provides the client with key material that the RS uses. This 1877 can either be a common symmetric PoP-key, or an asymmetric key used 1878 by the RS to authenticate towards the client. Since there is 1879 currently no expiration metadata associated to those keys, the client 1880 has no way of knowing if these keys are still valid. This may lead 1881 to situations where the client sends requests containing sensitive 1882 information to the RS using a key that is expired and possibly in the 1883 hands of an attacker, or accepts responses from the RS that are not 1884 properly protected and could possibly have been forged by an 1885 attacker. 1887 In order to prevent this, the client must assume that those keys are 1888 only valid as long as the related access token is. Since the access 1889 token is opaque to the client, one of the following methods MUST be 1890 used to inform the client about the validity of an access token: 1892 o The client knows a default validity time for all tokens it is 1893 using (i.e. how long a token is valid after being issued). This 1894 information could be provisioned to the client when it is 1895 registered at the AS, or published by the AS in a way that the 1896 client can query. 1898 o The AS informs the client about the token validity using the 1899 "expires_in" parameter in the Access Information. 1901 A client that is not able to obtain information about the expiration 1902 of a token MUST NOT use this token. 1904 6. Security Considerations 1906 Security considerations applicable to authentication and 1907 authorization in RESTful environments provided in OAuth 2.0 [RFC6749] 1908 apply to this work. Furthermore [RFC6819] provides additional 1909 security considerations for OAuth which apply to IoT deployments as 1910 well. If the introspection endpoint is used, the security 1911 considerations from [RFC7662] also apply. 1913 The following subsections address issues specific to this document 1914 and it's use in constrained environments. 1916 6.1. Protecting Tokens 1918 A large range of threats can be mitigated by protecting the contents 1919 of the access token by using a digital signature or a keyed message 1920 digest (MAC) or an Authenticated Encryption with Associated Data 1921 (AEAD) algorithm. Consequently, the token integrity protection MUST 1922 be applied to prevent the token from being modified, particularly 1923 since it contains a reference to the symmetric key or the asymmetric 1924 key used for proof-of-possession. If the access token contains the 1925 symmetric key, this symmetric key MUST be encrypted by the 1926 authorization server so that only the resource server can decrypt it. 1927 Note that using an AEAD algorithm is preferable over using a MAC 1928 unless the token needs to be publicly readable. 1930 If the token is intended for multiple recipients (i.e. an audience 1931 that is a group), integrity protection of the token with a symmetric 1932 key, shared between the AS and the recipients, is not sufficient, 1933 since any of the recipients could modify the token undetected by the 1934 other recipients. Therefore a token with a multi-recipient audience 1935 MUST be protected with an asymmetric signature. 1937 It is important for the authorization server to include the identity 1938 of the intended recipient (the audience), typically a single resource 1939 server (or a list of resource servers), in the token. The same 1940 shared secret MUST NOT be used as proof-of-possession key with 1941 multiple resource servers since the benefit from using the proof-of- 1942 possession concept is then significantly reduced. 1944 If clients are capable of doing so, they should frequently request 1945 fresh access tokens, as this allows the AS to keep the lifetime of 1946 the tokens short. This allows the AS to use shorter proof-of- 1947 possession key sizes, which translate to a performance benefit for 1948 the client and for the resource server. Shorter keys also lead to 1949 shorter messages (particularly with asymmetric keying material). 1951 When authorization servers bind symmetric keys to access tokens, they 1952 SHOULD scope these access tokens to a specific permission. 1954 In certain situations it may be necessary to revoke an access token 1955 that is still valid. Client-initiated revocation is specified in 1956 [RFC7009] for OAuth 2.0. Other revocation mechanisms are currently 1957 not specified, as the underlying assumption in OAuth is that access 1958 tokens are issued with a relatively short lifetime. This may not 1959 hold true for disconnected constrained devices, needing access tokens 1960 with relatively long lifetimes, and would therefore necessitate 1961 further standardization work that is out of scope for this document. 1963 6.2. Communication Security 1965 Communication with the authorization server MUST use confidentiality 1966 protection. This step is extremely important since the client or the 1967 RS may obtain the proof-of-possession key from the authorization 1968 server for use with a specific access token. Not using 1969 confidentiality protection exposes this secret (and the access token) 1970 to an eavesdropper thereby completely negating proof-of-possession 1971 security. Profiles MUST specify how communication security according 1972 to the requirements in Section 5 is provided. 1974 Additional protection for the access token can be applied by 1975 encrypting it, for example encryption of CWTs is specified in 1976 Section 5.1 of [RFC8392]. Such additional protection can be 1977 necessary if the token is later transferred over an insecure 1978 connection (e.g. when it is sent to the authz-info endpoint). 1980 Developers MUST ensure that the ephemeral credentials (i.e., the 1981 private key or the session key) are not leaked to third parties. An 1982 adversary in possession of the ephemeral credentials bound to the 1983 access token will be able to impersonate the client. Be aware that 1984 this is a real risk with many constrained environments, since 1985 adversaries can often easily get physical access to the devices. 1986 This risk can also be mitigated to some extent by making sure that 1987 keys are refreshed more frequently. 1989 6.3. Long-Term Credentials 1991 Both clients and RSs have long-term credentials that are used to 1992 secure communications, and authenticate to the AS. These credentials 1993 need to be protected against unauthorized access. In constrained 1994 devices, deployed in publicly accessible places, such protection can 1995 be difficult to achieve without specialized hardware (e.g. secure key 1996 storage memory). 1998 If credentials are lost or compromised, the operator of the affected 1999 devices needs to have procedures to invalidate any access these 2000 credentials give and to revoke tokens linked to such credentials. 2001 The loss of a credential linked to a specific device MUST NOT lead to 2002 a compromise of other credentials not linked to that device, 2003 therefore secret keys used for authentication MUST NOT be shared 2004 between more than two parties. 2006 Operators of clients or RS SHOULD have procedures in place to replace 2007 credentials that are suspected to have been compromised or that have 2008 been lost. 2010 Operators also SHOULD have procedures for decommissioning devices, 2011 that include securely erasing credentials and other security critical 2012 material in the devices being decommissioned. 2014 6.4. Unprotected AS Request Creation Hints 2016 Initially, no secure channel exists to protect the communication 2017 between C and RS. Thus, C cannot determine if the AS Request 2018 Creation Hints contained in an unprotected response from RS to an 2019 unauthorized request (see Section 5.3) are authentic. C therefore 2020 MUST determine if an AS is authorized to provide access tokens for a 2021 certain RS. 2023 A compromised RS may use the hints for attempting to trick a client 2024 into contacting an AS that is not supposed to be in charge of that 2025 RS. Therefore, C must not communicate with an AS if it cannot 2026 determine that this AS has the authority to issue access tokens for 2027 this RS. Otherwise, a compromised RS may use this to perform a 2028 denial of service attack against a specific AS, by redirecting a 2029 large number of client requests to that AS. 2031 6.5. Minimal security requirements for communication 2033 This section summarizes the minimal requirements for the 2034 communication security of the different protocol interactions. 2036 C-AS All communication between the client and the Authorization 2037 Server MUST be encrypted, integrity and replay protected. 2038 Furthermore responses from the AS to the client MUST be bound to 2039 the client's request to avoid attacks where the attacker swaps the 2040 intended response for an older one valid for a previous request. 2041 This requires that the client and the Authorization Server have 2042 previously exchanged either a shared secret or their public keys 2043 in order to negotiate a secure communication. Furthermore the 2044 client MUST be able to determine whether an AS has the authority 2045 to issue access tokens for a certain RS. This can for example be 2046 done through pre-configured lists, or through an online lookup 2047 mechanism that in turn also must be secured. 2049 RS-AS The communication between the Resource Server and the 2050 Authorization Server via the introspection endpoint MUST be 2051 encrypted, integrity and replay protected. Furthermore responses 2052 from the AS to the RS MUST be bound to the RS's request. This 2053 requires that the RS and the Authorization Server have previously 2054 exchanged either a shared secret, or their public keys in order to 2055 negotiate a secure communication. Furthermore the RS MUST be able 2056 to determine whether an AS has the authority to issue access 2057 tokens itself. This is usually configured out of band, but could 2058 also be performed through an online lookup mechanism provided that 2059 it is also secured in the same way. 2061 C-RS The initial communication between the client and the Resource 2062 Server can not be secured in general, since the RS is not in 2063 possession of on access token for that client, which would carry 2064 the necessary parameters. If both parties support DTLS without 2065 client authentication it is RECOMMEND to use this mechanism for 2066 protecting the initial communication. After the client has 2067 successfully transmitted the access token to the RS, a secure 2068 communication protocol MUST be established between client and RS 2069 for the actual resource request. This protocol MUST provide 2070 confidentiality, integrity and replay protection as well as a 2071 binding between requests and responses. This requires that the 2072 client learned either the RS's public key or received a symmetric 2073 proof-of-possession key bound to the access token from the AS. 2074 The RS must have learned either the client's public key or a 2075 shared symmetric key from the claims in the token or an 2076 introspection request. Since ACE does not provide profile 2077 negotiation between C and RS, the client MUST have learned what 2078 profile the RS supports (e.g. from the AS or pre-configured) and 2079 initiate the communication accordingly. 2081 6.6. Token Freshness and Expiration 2083 An RS that is offline faces the problem of clock drift. Since it 2084 cannot synchronize its clock with the AS, it may be tricked into 2085 accepting old access tokens that are no longer valid or have been 2086 compromised. In order to prevent this, an RS may use the nonce-based 2087 mechanism defined in Section 5.3 to ensure freshness of an Access 2088 Token subsequently presented to this RS. 2090 Another problem with clock drift is that evaluating the standard 2091 token expiration claim "exp" can give unpredictable results. 2093 Acceptable ranges of clock drift are highly dependent on the concrete 2094 application. Important factors are how long access tokens are valid, 2095 and how critical timely expiration of access token is. 2097 The expiration mechanism implemented by the "exi" claim, based on the 2098 first time the RS sees the token was defined to provide a more 2099 predictable alternative. The "exi" approach has some drawbacks that 2100 need to be considered: 2102 A malicious client may hold back tokens with the "exi" claim in 2103 order to prolong their lifespan. 2105 If an RS loses state (e.g. due to an unscheduled reboot), it may 2106 loose the current values of counters tracking the "exi" claims of 2107 tokens it is storing. 2109 The first drawback is inherent to the deployment scenario and the 2110 "exi" solution. It can therefore not be mitigated without requiring 2111 the the RS be online at times. The second drawback can be mitigated 2112 by regularly storing the value of "exi" counters to persistent 2113 memory. 2115 6.7. Combining profiles 2117 There may be use cases were different profiles of this framework are 2118 combined. For example, an MQTT-TLS profile is used between the 2119 client and the RS in combination with a CoAP-DTLS profile for 2120 interactions between the client and the AS. The security of a 2121 profile MUST NOT depend on the assumption that the profile is used 2122 for all the different types of interactions in this framework. 2124 6.8. Unprotected Information 2126 Communication with the authz-info endpoint, as well as the various 2127 error responses defined in this framework, all potentially include 2128 sending information over an unprotected channel. These messages may 2129 leak information to an adversary, or may be manipulated by active 2130 attackers to induce incorrect behavior. For example error responses 2131 for requests to the Authorization Information endpoint can reveal 2132 information about an otherwise opaque access token to an adversary 2133 who has intercepted this token. 2135 As far as error messages are concerned, this framework is written 2136 under the assumption that, in general, the benefits of detailed error 2137 messages outweigh the risk due to information leakage. For 2138 particular use cases, where this assessment does not apply, detailed 2139 error messages can be replaced by more generic ones. 2141 In some scenarios it may be possible to protect the communication 2142 with the authz-info endpoint (e.g. through DTLS with only server-side 2143 authentication). In cases where this is not possible this framework 2144 RECOMMENDS to use encrypted CWTs or tokens that are opaque references 2145 and need to be subjected to introspection by the RS. 2147 If the initial unauthorized resource request message (see 2148 Section 5.2) is used, the client MUST make sure that it is not 2149 sending sensitive content in this request. While GET and DELETE 2150 requests only reveal the target URI of the resource, POST and PUT 2151 requests would reveal the whole payload of the intended operation. 2153 Since the client is not authenticated at the point when it is 2154 submitting an access token to the authz-info endpoint, attackers may 2155 be pretending to be a client and trying to trick an RS to use an 2156 obsolete profile that in turn specifies a vulnerable security 2157 mechanism via the authz-info endpoint. Such an attack would require 2158 a valid access token containing an "ace_profile" claim requesting the 2159 use of said obsolete profile. Resource Owners should update the 2160 configuration of their RS's to prevent them from using such obsolete 2161 profiles. 2163 6.9. Identifying audiences 2165 The audience claim as defined in [RFC7519] and the equivalent 2166 "audience" parameter from [RFC8693] are intentionally vague on how to 2167 match the audience value to a specific RS. This is intended to allow 2168 application specific semantics to be used. This section attempts to 2169 give some general guidance for the use of audiences in constrained 2170 environments. 2172 URLs are not a good way of identifying mobile devices that can switch 2173 networks and thus be associated with new URLs. If the audience 2174 represents a single RS, and asymmetric keys are used, the RS can be 2175 uniquely identified by a hash of its public key. If this approach is 2176 used this framework RECOMMENDS to apply the procedure from section 3 2177 of [RFC6920]. 2179 If the audience addresses a group of resource servers, the mapping of 2180 group identifier to individual RS has to be provisioned to each RS 2181 before the group-audience is usable. Managing dynamic groups could 2182 be an issue, if any RS is not always reachable when the groups' 2183 memberships change. Furthermore, issuing access tokens bound to 2184 symmetric proof-of-possession keys that apply to a group-audience is 2185 problematic, as an RS that is in possession of the access token can 2186 impersonate the client towards the other RSs that are part of the 2187 group. It is therefore NOT RECOMMENDED to issue access tokens bound 2188 to a group audience and symmetric proof-of possession keys. 2190 Even the client must be able to determine the correct values to put 2191 into the "audience" parameter, in order to obtain a token for the 2192 intended RS. Errors in this process can lead to the client 2193 inadvertently obtaining a token for the wrong RS. The correct values 2194 for "audience" can either be provisioned to the client as part of its 2195 configuration, or dynamically looked up by the client in some 2196 directory. In the latter case the integrity and correctness of the 2197 directory data must be assured. Note that the "audience" hint 2198 provided by the RS as part of the "AS Request Creation Hints" 2199 Section 5.3 is not typically source authenticated and integrity 2200 protected, and should therefore not be treated a trusted value. 2202 6.10. Denial of service against or with Introspection 2204 The optional introspection mechanism provided by OAuth and supported 2205 in the ACE framework allows for two types of attacks that need to be 2206 considered by implementers. 2208 First, an attacker could perform a denial of service attack against 2209 the introspection endpoint at the AS in order to prevent validation 2210 of access tokens. To maintain the security of the system, an RS that 2211 is configured to use introspection MUST NOT allow access based on a 2212 token for which it couldn't reach the introspection endpoint. 2214 Second, an attacker could use the fact that an RS performs 2215 introspection to perform a denial of service attack against that RS 2216 by repeatedly sending tokens to its authz-info endpoint that require 2217 an introspection call. RS can mitigate such attacks by implementing 2218 rate limits on how many introspection requests they perform in a 2219 given time interval for a certain client IP address submitting tokens 2220 to /authz-info. When that limit has been reached, incoming requests 2221 from that address are rejected for a certain amount of time. A 2222 general rate limit on the introspection requests should also be 2223 considered, to mitigate distributed attacks. 2225 7. Privacy Considerations 2227 Implementers and users should be aware of the privacy implications of 2228 the different possible deployments of this framework. 2230 The AS is in a very central position and can potentially learn 2231 sensitive information about the clients requesting access tokens. If 2232 the client credentials grant is used, the AS can track what kind of 2233 access the client intends to perform. With other grants this can be 2234 prevented by the Resource Owner. To do so, the resource owner needs 2235 to bind the grants it issues to anonymous, ephemeral credentials that 2236 do not allow the AS to link different grants and thus different 2237 access token requests by the same client. 2239 The claims contained in a token can reveal privacy sensitive 2240 information about the client and the RS to any party having access to 2241 them (whether by processing the content of a self-contained token or 2242 by introspection). The AS SHOULD be configured to minimize the 2243 information about clients and RSs disclosed in the tokens it issues. 2245 If tokens are only integrity protected and not encrypted, they may 2246 reveal information to attackers listening on the wire, or able to 2247 acquire the access tokens in some other way. In the case of CWTs the 2248 token may, e.g., reveal the audience, the scope and the confirmation 2249 method used by the client. The latter may reveal the identity of the 2250 device or application running the client. This may be linkable to 2251 the identity of the person using the client (if there is a person and 2252 not a machine-to-machine interaction). 2254 Clients using asymmetric keys for proof-of-possession should be aware 2255 of the consequences of using the same key pair for proof-of- 2256 possession towards different RSs. A set of colluding RSs or an 2257 attacker able to obtain the access tokens will be able to link the 2258 requests, or even to determine the client's identity. 2260 An unprotected response to an unauthorized request (see Section 5.3) 2261 may disclose information about RS and/or its existing relationship 2262 with C. It is advisable to include as little information as possible 2263 in an unencrypted response. Even the absolute URI of the AS may 2264 reveal sensitive information about the service that RS provides. 2265 Developers must ensure that the RS does not disclose information that 2266 has an impact on the privacy of the stakeholders in the AS Request 2267 Creation Hints. They may choose to use a different mechanism for the 2268 discovery of the AS if necessary. If means of encrypting 2269 communication between C and RS already exist, more detailed 2270 information may be included with an error response to provide C with 2271 sufficient information to react on that particular error. 2273 8. IANA Considerations 2275 This document creates several registries with a registration policy 2276 of "Expert Review"; guidelines to the experts are given in 2277 Section 8.17. 2279 8.1. ACE Authorization Server Request Creation Hints 2281 This specification establishes the IANA "ACE Authorization Server 2282 Request Creation Hints" registry. The registry has been created to 2283 use the "Expert Review" registration procedure [RFC8126]. It should 2284 be noted that, in addition to the expert review, some portions of the 2285 registry require a specification, potentially a Standards Track RFC, 2286 be supplied as well. 2288 The columns of the registry are: 2290 Name The name of the parameter 2292 CBOR Key CBOR map key for the parameter. Different ranges of values 2293 use different registration policies [RFC8126]. Integer values 2294 from -256 to 255 are designated as Standards Action. Integer 2295 values from -65536 to -257 and from 256 to 65535 are designated as 2296 Specification Required. Integer values greater than 65535 are 2297 designated as Expert Review. Integer values less than -65536 are 2298 marked as Private Use. 2300 Value Type The CBOR data types allowable for the values of this 2301 parameter. 2303 Reference This contains a pointer to the public specification of the 2304 request creation hint abbreviation, if one exists. 2306 This registry will be initially populated by the values in Figure 2. 2307 The Reference column for all of these entries will be this document. 2309 8.2. CoRE Resource Type registry 2311 IANA is requested to register a new Resource Type (rt=) Link Target 2312 Attribute in the "Resource Type (rt=) Link Target Attribute Values" 2313 subregistry under the "Constrained RESTful Environments (CoRE) 2314 Parameters" [IANA.CoreParameters] registry: 2316 rt="ace.ai". This resource type describes an ACE-OAuth authz-info 2317 endpoint resource. 2319 Specific ACE-OAuth profiles can use this common resource type for 2320 defining their profile-specific discovery processes. 2322 8.3. OAuth Extensions Error Registration 2324 This specification registers the following error values in the OAuth 2325 Extensions Error registry [IANA.OAuthExtensionsErrorRegistry]. 2327 o Error name: "unsupported_pop_key" 2328 o Error usage location: token error response 2329 o Related protocol extension: [this document] 2330 o Change Controller: IESG 2331 o Specification document(s): Section 5.8.3 of [this document] 2333 o Error name: "incompatible_ace_profiles" 2334 o Error usage location: token error response 2335 o Related protocol extension: [this document] 2336 o Change Controller: IESG 2337 o Specification document(s): Section 5.8.3 of [this document] 2339 8.4. OAuth Error Code CBOR Mappings Registry 2341 This specification establishes the IANA "OAuth Error Code CBOR 2342 Mappings" registry. The registry has been created to use the "Expert 2343 Review" registration procedure [RFC8126], except for the value range 2344 designated for private use. 2346 The columns of the registry are: 2348 Name The OAuth Error Code name, refers to the name in Section 5.2. 2349 of [RFC6749], e.g., "invalid_request". 2350 CBOR Value CBOR abbreviation for this error code. Integer values 2351 less than -65536 are marked as "Private Use", all other values use 2352 the registration policy "Expert Review" [RFC8126]. 2353 Reference This contains a pointer to the public specification of the 2354 error code abbreviation, if one exists. 2356 This registry will be initially populated by the values in Figure 10. 2357 The Reference column for all of these entries will be this document. 2359 8.5. OAuth Grant Type CBOR Mappings 2361 This specification establishes the IANA "OAuth Grant Type CBOR 2362 Mappings" registry. The registry has been created to use the "Expert 2363 Review" registration procedure [RFC8126], except for the value range 2364 designated for private use. 2366 The columns of this registry are: 2368 Name The name of the grant type as specified in Section 1.3 of 2369 [RFC6749]. 2370 CBOR Value CBOR abbreviation for this grant type. Integer values 2371 less than -65536 are marked as "Private Use", all other values use 2372 the registration policy "Expert Review" [RFC8126]. 2373 Reference This contains a pointer to the public specification of the 2374 grant type abbreviation, if one exists. 2375 Original Specification This contains a pointer to the public 2376 specification of the grant type, if one exists. 2378 This registry will be initially populated by the values in Figure 11. 2379 The Reference column for all of these entries will be this document. 2381 8.6. OAuth Access Token Types 2383 This section registers the following new token type in the "OAuth 2384 Access Token Types" registry [IANA.OAuthAccessTokenTypes]. 2386 o Type name: "PoP" 2387 o Additional Token Endpoint Response Parameters: "cnf", "rs_cnf" see 2388 section 3.3 of [I-D.ietf-ace-oauth-params]. 2389 o HTTP Authentication Scheme(s): N/A 2390 o Change Controller: IETF 2391 o Specification document(s): [this document] 2393 8.7. OAuth Access Token Type CBOR Mappings 2395 This specification established the IANA "OAuth Access Token Type CBOR 2396 Mappings" registry. The registry has been created to use the "Expert 2397 Review" registration procedure [RFC8126], except for the value range 2398 designated for private use. 2400 The columns of this registry are: 2402 Name The name of token type as registered in the OAuth Access Token 2403 Types registry, e.g., "Bearer". 2404 CBOR Value CBOR abbreviation for this token type. Integer values 2405 less than -65536 are marked as "Private Use", all other values use 2406 the registration policy "Expert Review" [RFC8126]. 2407 Reference This contains a pointer to the public specification of the 2408 OAuth token type abbreviation, if one exists. 2409 Original Specification This contains a pointer to the public 2410 specification of the OAuth token type, if one exists. 2412 8.7.1. Initial Registry Contents 2414 o Name: "Bearer" 2415 o Value: 1 2416 o Reference: [this document] 2417 o Original Specification: [RFC6749] 2419 o Name: "PoP" 2420 o Value: 2 2421 o Reference: [this document] 2422 o Original Specification: [this document] 2424 8.8. ACE Profile Registry 2426 This specification establishes the IANA "ACE Profile" registry. The 2427 registry has been created to use the "Expert Review" registration 2428 procedure [RFC8126]. It should be noted that, in addition to the 2429 expert review, some portions of the registry require a specification, 2430 potentially a Standards Track RFC, be supplied as well. 2432 The columns of this registry are: 2434 Name The name of the profile, to be used as value of the profile 2435 attribute. 2436 Description Text giving an overview of the profile and the context 2437 it is developed for. 2438 CBOR Value CBOR abbreviation for this profile name. Different 2439 ranges of values use different registration policies [RFC8126]. 2440 Integer values from -256 to 255 are designated as Standards 2441 Action. Integer values from -65536 to -257 and from 256 to 65535 2442 are designated as Specification Required. Integer values greater 2443 than 65535 are designated as "Expert Review". Integer values less 2444 than -65536 are marked as Private Use. 2445 Reference This contains a pointer to the public specification of the 2446 profile abbreviation, if one exists. 2448 This registry will be initially empty and will be populated by the 2449 registrations from the ACE framework profiles. 2451 8.9. OAuth Parameter Registration 2453 This specification registers the following parameter in the "OAuth 2454 Parameters" registry [IANA.OAuthParameters]: 2456 o Name: "ace_profile" 2457 o Parameter Usage Location: token response 2458 o Change Controller: IESG 2459 o Reference: Section 5.8.2 and Section 5.8.4.3 of [this document] 2461 8.10. OAuth Parameters CBOR Mappings Registry 2463 This specification establishes the IANA "OAuth Parameters CBOR 2464 Mappings" registry. The registry has been created to use the "Expert 2465 Review" registration procedure [RFC8126], except for the value range 2466 designated for private use. 2468 The columns of this registry are: 2470 Name The OAuth Parameter name, refers to the name in the OAuth 2471 parameter registry, e.g., "client_id". 2472 CBOR Key CBOR map key for this parameter. Integer values less than 2473 -65536 are marked as "Private Use", all other values use the 2474 registration policy "Expert Review" [RFC8126]. 2475 Value Type The allowable CBOR data types for values of this 2476 parameter. 2477 Reference This contains a pointer to the public specification of the 2478 OAuth parameter abbreviation, if one exists. 2480 This registry will be initially populated by the values in Figure 12. 2481 The Reference column for all of these entries will be this document. 2483 8.11. OAuth Introspection Response Parameter Registration 2485 This specification registers the following parameters in the OAuth 2486 Token Introspection Response registry 2487 [IANA.TokenIntrospectionResponse]. 2489 o Name: "ace_profile" 2490 o Description: The ACE profile used between client and RS. 2491 o Change Controller: IESG 2492 o Reference: Section 5.9.2 of [this document] 2494 o Name: "cnonce" 2495 o Description: "client-nonce". A nonce previously provided to the 2496 AS by the RS via the client. Used to verify token freshness when 2497 the RS cannot synchronize its clock with the AS. 2498 o Change Controller: IESG 2499 o Reference: Section 5.9.2 of [this document] 2501 o Name: "exi" 2502 o Description: "Expires in". Lifetime of the token in seconds from 2503 the time the RS first sees it. Used to implement a weaker from of 2504 token expiration for devices that cannot synchronize their 2505 internal clocks. 2506 o Change Controller: IESG 2507 o Reference: Section 5.9.2 of [this document] 2509 8.12. OAuth Token Introspection Response CBOR Mappings Registry 2511 This specification establishes the IANA "OAuth Token Introspection 2512 Response CBOR Mappings" registry. The registry has been created to 2513 use the "Expert Review" registration procedure [RFC8126], except for 2514 the value range designated for private use. 2516 The columns of this registry are: 2518 Name The OAuth Parameter name, refers to the name in the OAuth 2519 parameter registry, e.g., "client_id". 2520 CBOR Key CBOR map key for this parameter. Integer values less than 2521 -65536 are marked as "Private Use", all other values use the 2522 registration policy "Expert Review" [RFC8126]. 2523 Value Type The allowable CBOR data types for values of this 2524 parameter. 2525 Reference This contains a pointer to the public specification of the 2526 introspection response parameter abbreviation, if one exists. 2528 This registry will be initially populated by the values in Figure 16. 2529 The Reference column for all of these entries will be this document. 2531 Note that the mappings of parameters corresponding to claim names 2532 intentionally coincide with the CWT claim name mappings from 2533 [RFC8392]. 2535 8.13. JSON Web Token Claims 2537 This specification registers the following new claims in the JSON Web 2538 Token (JWT) registry of JSON Web Token Claims 2539 [IANA.JsonWebTokenClaims]: 2541 o Claim Name: "ace_profile" 2542 o Claim Description: The ACE profile a token is supposed to be used 2543 with. 2544 o Change Controller: IESG 2545 o Reference: Section 5.10 of [this document] 2547 o Claim Name: "cnonce" 2548 o Claim Description: "client-nonce". A nonce previously provided to 2549 the AS by the RS via the client. Used to verify token freshness 2550 when the RS cannot synchronize its clock with the AS. 2551 o Change Controller: IESG 2552 o Reference: Section 5.10 of [this document] 2554 o Claim Name: "exi" 2555 o Claim Description: "Expires in". Lifetime of the token in seconds 2556 from the time the RS first sees it. Used to implement a weaker 2557 from of token expiration for devices that cannot synchronize their 2558 internal clocks. 2559 o Change Controller: IESG 2560 o Reference: Section 5.10.3 of [this document] 2562 8.14. CBOR Web Token Claims 2564 This specification registers the following new claims in the "CBOR 2565 Web Token (CWT) Claims" registry [IANA.CborWebTokenClaims]. 2567 o Claim Name: "ace_profile" 2568 o Claim Description: The ACE profile a token is supposed to be used 2569 with. 2570 o JWT Claim Name: ace_profile 2571 o Claim Key: TBD (suggested: 38) 2572 o Claim Value Type(s): integer 2573 o Change Controller: IESG 2574 o Specification Document(s): Section 5.10 of [this document] 2576 o Claim Name: "cnonce" 2577 o Claim Description: The client-nonce sent to the AS by the RS via 2578 the client. 2579 o JWT Claim Name: cnonce 2580 o Claim Key: TBD (suggested: 39) 2581 o Claim Value Type(s): byte string 2582 o Change Controller: IESG 2583 o Specification Document(s): Section 5.10 of [this document] 2585 o Claim Name: "exi" 2586 o Claim Description: The expiration time of a token measured from 2587 when it was received at the RS in seconds. 2588 o JWT Claim Name: exi 2589 o Claim Key: TBD (suggested: 40) 2590 o Claim Value Type(s): integer 2591 o Change Controller: IESG 2592 o Specification Document(s): Section 5.10.3 of [this document] 2594 o Claim Name: "scope" 2595 o Claim Description: The scope of an access token as defined in 2596 [RFC6749]. 2597 o JWT Claim Name: scope 2598 o Claim Key: TBD (suggested: 9) 2599 o Claim Value Type(s): byte string or text string 2600 o Change Controller: IESG 2601 o Specification Document(s): Section 4.2 of [RFC8693] 2603 8.15. Media Type Registrations 2605 This specification registers the 'application/ace+cbor' media type 2606 for messages of the protocols defined in this document carrying 2607 parameters encoded in CBOR. This registration follows the procedures 2608 specified in [RFC6838]. 2610 Type name: application 2612 Subtype name: ace+cbor 2614 Required parameters: N/A 2616 Optional parameters: N/A 2618 Encoding considerations: Must be encoded as CBOR map containing the 2619 protocol parameters defined in [this document]. 2621 Security considerations: See Section 6 of [this document] 2623 Interoperability considerations: N/A 2625 Published specification: [this document] 2627 Applications that use this media type: The type is used by 2628 authorization servers, clients and resource servers that support the 2629 ACE framework as specified in [this document]. 2631 Fragment identifier considerations: N/A 2633 Additional information: N/A 2635 Person & email address to contact for further information: 2636 2638 Intended usage: COMMON 2640 Restrictions on usage: none 2642 Author: Ludwig Seitz 2644 Change controller: IESG 2646 8.16. CoAP Content-Format Registry 2648 This specification registers the following entry to the "CoAP 2649 Content-Formats" registry: 2651 Media Type: application/ace+cbor 2653 Encoding: - 2655 ID: TBD (suggested: 19) 2657 Reference: [this document] 2659 8.17. Expert Review Instructions 2661 All of the IANA registries established in this document are defined 2662 to use a registration policy of Expert Review. This section gives 2663 some general guidelines for what the experts should be looking for, 2664 but they are being designated as experts for a reason, so they should 2665 be given substantial latitude. 2667 Expert reviewers should take into consideration the following points: 2669 o Point squatting should be discouraged. Reviewers are encouraged 2670 to get sufficient information for registration requests to ensure 2671 that the usage is not going to duplicate one that is already 2672 registered, and that the point is likely to be used in 2673 deployments. The zones tagged as private use are intended for 2674 testing purposes and closed environments; code points in other 2675 ranges should not be assigned for testing. 2676 o Specifications are needed for the first-come, first-serve range if 2677 they are expected to be used outside of closed environments in an 2678 interoperable way. When specifications are not provided, the 2679 description provided needs to have sufficient information to 2680 identify what the point is being used for. 2681 o Experts should take into account the expected usage of fields when 2682 approving point assignment. The fact that there is a range for 2683 standards track documents does not mean that a standards track 2684 document cannot have points assigned outside of that range. The 2685 length of the encoded value should be weighed against how many 2686 code points of that length are left, the size of device it will be 2687 used on. 2688 o Since a high degree of overlap is expected between these 2689 registries and the contents of the OAuth parameters 2690 [IANA.OAuthParameters] registries, experts should require new 2691 registrations to maintain alignment with parameters from OAuth 2692 that have comparable functionality. Deviation from this alignment 2693 should only be allowed if there are functional differences, that 2694 are motivated by the use case and that cannot be easily or 2695 efficiently addressed by comparable OAuth parameters. 2697 9. Acknowledgments 2699 This document is a product of the ACE working group of the IETF. 2701 Thanks to Eve Maler for her contributions to the use of OAuth 2.0 and 2702 UMA in IoT scenarios, Robert Taylor for his discussion input, and 2703 Malisa Vucinic for his input on the predecessors of this proposal. 2705 Thanks to the authors of draft-ietf-oauth-pop-key-distribution, from 2706 where large parts of the security considerations where copied. 2708 Thanks to Stefanie Gerdes, Olaf Bergmann, and Carsten Bormann for 2709 contributing their work on AS discovery from draft-gerdes-ace-dcaf- 2710 authorize (see Section 5.1). 2712 Thanks to Jim Schaad and Mike Jones for their comprehensive reviews. 2714 Thanks to Benjamin Kaduk for his input on various questions related 2715 to this work. 2717 Thanks to Cigdem Sengul for some very useful review comments. 2719 Thanks to Carsten Bormann for contributing the text for the CoRE 2720 Resource Type registry. 2722 Ludwig Seitz and Goeran Selander worked on this document as part of 2723 the CelticPlus project CyberWI, with funding from Vinnova. Ludwig 2724 Seitz was also received further funding for this work by Vinnova in 2725 the context of the CelticNext project Critisec. 2727 10. References 2729 10.1. Normative References 2731 [I-D.ietf-ace-oauth-params] 2732 Seitz, L., "Additional OAuth Parameters for Authorization 2733 in Constrained Environments (ACE)", draft-ietf-ace-oauth- 2734 params-13 (work in progress), April 2020. 2736 [IANA.CborWebTokenClaims] 2737 IANA, "CBOR Web Token (CWT) Claims", 2738 . 2741 [IANA.CoreParameters] 2742 IANA, "Constrained RESTful Environments (CoRE) 2743 Parameters", . 2746 [IANA.JsonWebTokenClaims] 2747 IANA, "JSON Web Token Claims", 2748 . 2750 [IANA.OAuthAccessTokenTypes] 2751 IANA, "OAuth Access Token Types", 2752 . 2755 [IANA.OAuthExtensionsErrorRegistry] 2756 IANA, "OAuth Extensions Error Registry", 2757 . 2760 [IANA.OAuthParameters] 2761 IANA, "OAuth Parameters", 2762 . 2765 [IANA.TokenIntrospectionResponse] 2766 IANA, "OAuth Token Introspection Response", 2767 . 2770 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2771 Requirement Levels", BCP 14, RFC 2119, 2772 DOI 10.17487/RFC2119, March 1997, 2773 . 2775 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 2776 Resource Identifier (URI): Generic Syntax", STD 66, 2777 RFC 3986, DOI 10.17487/RFC3986, January 2005, 2778 . 2780 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 2781 FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, 2782 . 2784 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 2785 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 2786 January 2012, . 2788 [RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework", 2789 RFC 6749, DOI 10.17487/RFC6749, October 2012, 2790 . 2792 [RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization 2793 Framework: Bearer Token Usage", RFC 6750, 2794 DOI 10.17487/RFC6750, October 2012, 2795 . 2797 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 2798 Specifications and Registration Procedures", BCP 13, 2799 RFC 6838, DOI 10.17487/RFC6838, January 2013, 2800 . 2802 [RFC6920] Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B., 2803 Keranen, A., and P. Hallam-Baker, "Naming Things with 2804 Hashes", RFC 6920, DOI 10.17487/RFC6920, April 2013, 2805 . 2807 [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object 2808 Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, 2809 October 2013, . 2811 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 2812 Application Protocol (CoAP)", RFC 7252, 2813 DOI 10.17487/RFC7252, June 2014, 2814 . 2816 [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token 2817 (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, 2818 . 2820 [RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection", 2821 RFC 7662, DOI 10.17487/RFC7662, October 2015, 2822 . 2824 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2825 Writing an IANA Considerations Section in RFCs", BCP 26, 2826 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2827 . 2829 [RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", 2830 RFC 8152, DOI 10.17487/RFC8152, July 2017, 2831 . 2833 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2834 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2835 May 2017, . 2837 [RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, 2838 "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, 2839 May 2018, . 2841 [RFC8693] Jones, M., Nadalin, A., Campbell, B., Ed., Bradley, J., 2842 and C. Mortimore, "OAuth 2.0 Token Exchange", RFC 8693, 2843 DOI 10.17487/RFC8693, January 2020, 2844 . 2846 [RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H. 2847 Tschofenig, "Proof-of-Possession Key Semantics for CBOR 2848 Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March 2849 2020, . 2851 10.2. Informative References 2853 [BLE] Bluetooth SIG, "Bluetooth Core Specification v5.1", 2854 Section 4.4, January 2019, 2855 . 2858 [I-D.erdtman-ace-rpcc] 2859 Seitz, L. and S. Erdtman, "Raw-Public-Key and Pre-Shared- 2860 Key as OAuth client credentials", draft-erdtman-ace- 2861 rpcc-02 (work in progress), October 2017. 2863 [I-D.ietf-quic-transport] 2864 Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed 2865 and Secure Transport", draft-ietf-quic-transport-32 (work 2866 in progress), October 2020. 2868 [I-D.ietf-tls-dtls13] 2869 Rescorla, E., Tschofenig, H., and N. Modadugu, "The 2870 Datagram Transport Layer Security (DTLS) Protocol Version 2871 1.3", draft-ietf-tls-dtls13-39 (work in progress), 2872 November 2020. 2874 [Margi10impact] 2875 Margi, C., de Oliveira, B., de Sousa, G., Simplicio Jr, 2876 M., Barreto, P., Carvalho, T., Naeslund, M., and R. Gold, 2877 "Impact of Operating Systems on Wireless Sensor Networks 2878 (Security) Applications and Testbeds", Proceedings of 2879 the 19th International Conference on Computer 2880 Communications and Networks (ICCCN), August 2010. 2882 [MQTT5.0] Banks, A., Briggs, E., Borgendale, K., and R. Gupta, "MQTT 2883 Version 5.0", OASIS Standard, March 2019, 2884 . 2887 [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link 2888 Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, 2889 . 2891 [RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0 2892 Threat Model and Security Considerations", RFC 6819, 2893 DOI 10.17487/RFC6819, January 2013, 2894 . 2896 [RFC7009] Lodderstedt, T., Ed., Dronia, S., and M. Scurtescu, "OAuth 2897 2.0 Token Revocation", RFC 7009, DOI 10.17487/RFC7009, 2898 August 2013, . 2900 [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for 2901 Constrained-Node Networks", RFC 7228, 2902 DOI 10.17487/RFC7228, May 2014, 2903 . 2905 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 2906 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 2907 DOI 10.17487/RFC7231, June 2014, 2908 . 2910 [RFC7521] Campbell, B., Mortimore, C., Jones, M., and Y. Goland, 2911 "Assertion Framework for OAuth 2.0 Client Authentication 2912 and Authorization Grants", RFC 7521, DOI 10.17487/RFC7521, 2913 May 2015, . 2915 [RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext 2916 Transfer Protocol Version 2 (HTTP/2)", RFC 7540, 2917 DOI 10.17487/RFC7540, May 2015, 2918 . 2920 [RFC7591] Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and 2921 P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol", 2922 RFC 7591, DOI 10.17487/RFC7591, July 2015, 2923 . 2925 [RFC7641] Hartke, K., "Observing Resources in the Constrained 2926 Application Protocol (CoAP)", RFC 7641, 2927 DOI 10.17487/RFC7641, September 2015, 2928 . 2930 [RFC7744] Seitz, L., Ed., Gerdes, S., Ed., Selander, G., Mani, M., 2931 and S. Kumar, "Use Cases for Authentication and 2932 Authorization in Constrained Environments", RFC 7744, 2933 DOI 10.17487/RFC7744, January 2016, 2934 . 2936 [RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in 2937 the Constrained Application Protocol (CoAP)", RFC 7959, 2938 DOI 10.17487/RFC7959, August 2016, 2939 . 2941 [RFC8252] Denniss, W. and J. Bradley, "OAuth 2.0 for Native Apps", 2942 BCP 212, RFC 8252, DOI 10.17487/RFC8252, October 2017, 2943 . 2945 [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 2946 Interchange Format", STD 90, RFC 8259, 2947 DOI 10.17487/RFC8259, December 2017, 2948 . 2950 [RFC8414] Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0 2951 Authorization Server Metadata", RFC 8414, 2952 DOI 10.17487/RFC8414, June 2018, 2953 . 2955 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 2956 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 2957 . 2959 [RFC8516] Keranen, A., ""Too Many Requests" Response Code for the 2960 Constrained Application Protocol", RFC 8516, 2961 DOI 10.17487/RFC8516, January 2019, 2962 . 2964 [RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, 2965 "Object Security for Constrained RESTful Environments 2966 (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, 2967 . 2969 [RFC8628] Denniss, W., Bradley, J., Jones, M., and H. Tschofenig, 2970 "OAuth 2.0 Device Authorization Grant", RFC 8628, 2971 DOI 10.17487/RFC8628, August 2019, 2972 . 2974 Appendix A. Design Justification 2976 This section provides further insight into the design decisions of 2977 the solution documented in this document. Section 3 lists several 2978 building blocks and briefly summarizes their importance. The 2979 justification for offering some of those building blocks, as opposed 2980 to using OAuth 2.0 as is, is given below. 2982 Common IoT constraints are: 2984 Low Power Radio: 2986 Many IoT devices are equipped with a small battery which needs to 2987 last for a long time. For many constrained wireless devices, the 2988 highest energy cost is associated to transmitting or receiving 2989 messages (roughly by a factor of 10 compared to AES) 2990 [Margi10impact]. It is therefore important to keep the total 2991 communication overhead low, including minimizing the number and 2992 size of messages sent and received, which has an impact of choice 2993 on the message format and protocol. By using CoAP over UDP and 2994 CBOR encoded messages, some of these aspects are addressed. 2995 Security protocols contribute to the communication overhead and 2996 can, in some cases, be optimized. For example, authentication and 2997 key establishment may, in certain cases where security 2998 requirements allow, be replaced by provisioning of security 2999 context by a trusted third party, using transport or application 3000 layer security. 3002 Low CPU Speed: 3004 Some IoT devices are equipped with processors that are 3005 significantly slower than those found in most current devices on 3006 the Internet. This typically has implications on what timely 3007 cryptographic operations a device is capable of performing, which 3008 in turn impacts, e.g., protocol latency. Symmetric key 3009 cryptography may be used instead of the computationally more 3010 expensive public key cryptography where the security requirements 3011 so allow, but this may also require support for trusted-third- 3012 party-assisted secret key establishment using transport- or 3013 application-layer security. 3014 Small Amount of Memory: 3016 Microcontrollers embedded in IoT devices are often equipped with 3017 only a small amount of RAM and flash memory, which places 3018 limitations on what kind of processing can be performed and how 3019 much code can be put on those devices. To reduce code size, fewer 3020 and smaller protocol implementations can be put on the firmware of 3021 such a device. In this case, CoAP may be used instead of HTTP, 3022 symmetric-key cryptography instead of public-key cryptography, and 3023 CBOR instead of JSON. An authentication and key establishment 3024 protocol, e.g., the DTLS handshake, in comparison with assisted 3025 key establishment, also has an impact on memory and code 3026 footprints. 3028 User Interface Limitations: 3030 Protecting access to resources is both an important security as 3031 well as privacy feature. End users and enterprise customers may 3032 not want to give access to the data collected by their IoT device 3033 or to functions it may offer to third parties. Since the 3034 classical approach of requesting permissions from end users via a 3035 rich user interface does not work in many IoT deployment 3036 scenarios, these functions need to be delegated to user-controlled 3037 devices that are better suitable for such tasks, such as smart 3038 phones and tablets. 3040 Communication Constraints: 3042 In certain constrained settings an IoT device may not be able to 3043 communicate with a given device at all times. Devices may be 3044 sleeping, or just disconnected from the Internet because of 3045 general lack of connectivity in the area, for cost reasons, or for 3046 security reasons, e.g., to avoid an entry point for Denial-of- 3047 Service attacks. 3049 The communication interactions this framework builds upon (as 3050 shown graphically in Figure 1) may be accomplished using a variety 3051 of different protocols, and not all parts of the message flow are 3052 used in all applications due to the communication constraints. 3053 Deployments making use of CoAP are expected, but this framework is 3054 not limited to them. Other protocols such as HTTP, or even 3055 protocols such as Bluetooth Smart communication that do not 3056 necessarily use IP, could also be used. The latter raises the 3057 need for application layer security over the various interfaces. 3059 In the light of these constraints we have made the following design 3060 decisions: 3062 CBOR, COSE, CWT: 3064 This framework RECOMMENDS the use of CBOR [RFC7049] as data 3065 format. Where CBOR data needs to be protected, the use of COSE 3066 [RFC8152] is RECOMMENDED. Furthermore, where self-contained 3067 tokens are needed, this framework RECOMMENDS the use of CWT 3068 [RFC8392]. These measures aim at reducing the size of messages 3069 sent over the wire, the RAM size of data objects that need to be 3070 kept in memory and the size of libraries that devices need to 3071 support. 3073 CoAP: 3075 This framework RECOMMENDS the use of CoAP [RFC7252] instead of 3076 HTTP. This does not preclude the use of other protocols 3077 specifically aimed at constrained devices, like, e.g., Bluetooth 3078 Low Energy (see Section 3.2). This aims again at reducing the 3079 size of messages sent over the wire, the RAM size of data objects 3080 that need to be kept in memory and the size of libraries that 3081 devices need to support. 3083 Access Information: 3085 This framework defines the name "Access Information" for data 3086 concerning the RS that the AS returns to the client in an access 3087 token response (see Section 5.8.2). This aims at enabling 3088 scenarios where a powerful client, supporting multiple profiles, 3089 needs to interact with an RS for which it does not know the 3090 supported profiles and the raw public key. 3092 Proof-of-Possession: 3094 This framework makes use of proof-of-possession tokens, using the 3095 "cnf" claim [RFC8747]. A request parameter "cnf" and a Response 3096 parameter "cnf", both having a value space semantically and 3097 syntactically identical to the "cnf" claim, are defined for the 3098 token endpoint, to allow requesting and stating confirmation keys. 3099 This aims at making token theft harder. Token theft is 3100 specifically relevant in constrained use cases, as communication 3101 often passes through middle-boxes, which could be able to steal 3102 bearer tokens and use them to gain unauthorized access. 3104 Authz-Info endpoint: 3106 This framework introduces a new way of providing access tokens to 3107 an RS by exposing a authz-info endpoint, to which access tokens 3108 can be POSTed. This aims at reducing the size of the request 3109 message and the code complexity at the RS. The size of the 3110 request message is problematic, since many constrained protocols 3111 have severe message size limitations at the physical layer (e.g., 3112 in the order of 100 bytes). This means that larger packets get 3113 fragmented, which in turn combines badly with the high rate of 3114 packet loss, and the need to retransmit the whole message if one 3115 packet gets lost. Thus separating sending of the request and 3116 sending of the access tokens helps to reduce fragmentation. 3118 Client Credentials Grant: 3120 This framework RECOMMENDS the use of the client credentials grant 3121 for machine-to-machine communication use cases, where manual 3122 intervention of the resource owner to produce a grant token is not 3123 feasible. The intention is that the resource owner would instead 3124 pre-arrange authorization with the AS, based on the client's own 3125 credentials. The client can then (without manual intervention) 3126 obtain access tokens from the AS. 3128 Introspection: 3130 This framework RECOMMENDS the use of access token introspection in 3131 cases where the client is constrained in a way that it can not 3132 easily obtain new access tokens (i.e. it has connectivity issues 3133 that prevent it from communicating with the AS). In that case 3134 this framework RECOMMENDS the use of a long-term token, that could 3135 be a simple reference. The RS is assumed to be able to 3136 communicate with the AS, and can therefore perform introspection, 3137 in order to learn the claims associated with the token reference. 3138 The advantage of such an approach is that the resource owner can 3139 change the claims associated to the token reference without having 3140 to be in contact with the client, thus granting or revoking access 3141 rights. 3143 Appendix B. Roles and Responsibilities 3145 Resource Owner 3147 * Make sure that the RS is registered at the AS. This includes 3148 making known to the AS which profiles, token_type, scopes, and 3149 key types (symmetric/asymmetric) the RS supports. Also making 3150 it known to the AS which audience(s) the RS identifies itself 3151 with. 3152 * Make sure that clients can discover the AS that is in charge of 3153 the RS. 3154 * If the client-credentials grant is used, make sure that the AS 3155 has the necessary, up-to-date, access control policies for the 3156 RS. 3158 Requesting Party 3160 * Make sure that the client is provisioned the necessary 3161 credentials to authenticate to the AS. 3162 * Make sure that the client is configured to follow the security 3163 requirements of the Requesting Party when issuing requests 3164 (e.g., minimum communication security requirements, trust 3165 anchors). 3166 * Register the client at the AS. This includes making known to 3167 the AS which profiles, token_types, and key types (symmetric/ 3168 asymmetric) the client. 3170 Authorization Server 3172 * Register the RS and manage corresponding security contexts. 3173 * Register clients and authentication credentials. 3175 * Allow Resource Owners to configure and update access control 3176 policies related to their registered RSs. 3177 * Expose the token endpoint to allow clients to request tokens. 3178 * Authenticate clients that wish to request a token. 3179 * Process a token request using the authorization policies 3180 configured for the RS. 3181 * Optionally: Expose the introspection endpoint that allows RS's 3182 to submit token introspection requests. 3183 * If providing an introspection endpoint: Authenticate RSs that 3184 wish to get an introspection response. 3185 * If providing an introspection endpoint: Process token 3186 introspection requests. 3187 * Optionally: Handle token revocation. 3188 * Optionally: Provide discovery metadata. See [RFC8414] 3189 * Optionally: Handle refresh tokens. 3191 Client 3193 * Discover the AS in charge of the RS that is to be targeted with 3194 a request. 3195 * Submit the token request (see step (A) of Figure 1). 3197 + Authenticate to the AS. 3198 + Optionally (if not pre-configured): Specify which RS, which 3199 resource(s), and which action(s) the request(s) will target. 3200 + If raw public keys (rpk) or certificates are used, make sure 3201 the AS has the right rpk or certificate for this client. 3202 * Process the access token and Access Information (see step (B) 3203 of Figure 1). 3205 + Check that the Access Information provides the necessary 3206 security parameters (e.g., PoP key, information on 3207 communication security protocols supported by the RS). 3208 + Safely store the proof-of-possession key. 3209 + If provided by the AS: Safely store the refresh token. 3210 * Send the token and request to the RS (see step (C) of 3211 Figure 1). 3213 + Authenticate towards the RS (this could coincide with the 3214 proof of possession process). 3215 + Transmit the token as specified by the AS (default is to the 3216 authz-info endpoint, alternative options are specified by 3217 profiles). 3218 + Perform the proof-of-possession procedure as specified by 3219 the profile in use (this may already have been taken care of 3220 through the authentication procedure). 3221 * Process the RS response (see step (F) of Figure 1) of the RS. 3223 Resource Server 3225 * Expose a way to submit access tokens. By default this is the 3226 authz-info endpoint. 3227 * Process an access token. 3229 + Verify the token is from a recognized AS. 3230 + Check the token's integrity. 3231 + Verify that the token applies to this RS. 3232 + Check that the token has not expired (if the token provides 3233 expiration information). 3234 + Store the token so that it can be retrieved in the context 3235 of a matching request. 3237 Note: The order proposed here is not normative, any process 3238 that arrives at an equivalent result can be used. A noteworthy 3239 consideration is whether one can use cheap operations early on 3240 to quickly discard non-applicable or invalid tokens, before 3241 performing expensive cryptographic operations (e.g. doing an 3242 expiration check before verifying a signature). 3244 * Process a request. 3246 + Set up communication security with the client. 3247 + Authenticate the client. 3248 + Match the client against existing tokens. 3249 + Check that tokens belonging to the client actually authorize 3250 the requested action. 3251 + Optionally: Check that the matching tokens are still valid, 3252 using introspection (if this is possible.) 3253 * Send a response following the agreed upon communication 3254 security mechanism(s). 3255 * Safely store credentials such as raw public keys for 3256 authentication or proof-of-possession keys linked to access 3257 tokens. 3259 Appendix C. Requirements on Profiles 3261 This section lists the requirements on profiles of this framework, 3262 for the convenience of profile designers. 3264 o Optionally define new methods for the client to discover the 3265 necessary permissions and AS for accessing a resource, different 3266 from the one proposed in Section 5.1. Section 4 3267 o Optionally specify new grant types. Section 5.4 3268 o Optionally define the use of client certificates as client 3269 credential type. Section 5.5 3271 o Specify the communication protocol the client and RS the must use 3272 (e.g., CoAP). Section 5 and Section 5.8.4.3 3273 o Specify the security protocol the client and RS must use to 3274 protect their communication (e.g., OSCORE or DTLS). This must 3275 provide encryption, integrity and replay protection. 3276 Section 5.8.4.3 3277 o Specify how the client and the RS mutually authenticate. 3278 Section 4 3279 o Specify the proof-of-possession protocol(s) and how to select one, 3280 if several are available. Also specify which key types (e.g., 3281 symmetric/asymmetric) are supported by a specific proof-of- 3282 possession protocol. Section 5.8.4.2 3283 o Specify a unique ace_profile identifier. Section 5.8.4.3 3284 o If introspection is supported: Specify the communication and 3285 security protocol for introspection. Section 5.9 3286 o Specify the communication and security protocol for interactions 3287 between client and AS. This must provide encryption, integrity 3288 protection, replay protection and a binding between requests and 3289 responses. Section 5 and Section 5.8 3290 o Specify how/if the authz-info endpoint is protected, including how 3291 error responses are protected. Section 5.10.1 3292 o Optionally define other methods of token transport than the authz- 3293 info endpoint. Section 5.10.1 3295 Appendix D. Assumptions on AS knowledge about C and RS 3297 This section lists the assumptions on what an AS should know about a 3298 client and an RS in order to be able to respond to requests to the 3299 token and introspection endpoints. How this information is 3300 established is out of scope for this document. 3302 o The identifier of the client or RS. 3303 o The profiles that the client or RS supports. 3304 o The scopes that the RS supports. 3305 o The audiences that the RS identifies with. 3306 o The key types (e.g., pre-shared symmetric key, raw public key, key 3307 length, other key parameters) that the client or RS supports. 3308 o The types of access tokens the RS supports (e.g., CWT). 3309 o If the RS supports CWTs, the COSE parameters for the crypto 3310 wrapper (e.g., algorithm, key-wrap algorithm, key-length) that the 3311 RS supports. 3312 o The expiration time for access tokens issued to this RS (unless 3313 the RS accepts a default time chosen by the AS). 3314 o The symmetric key shared between client and AS (if any). 3315 o The symmetric key shared between RS and AS (if any). 3316 o The raw public key of the client or RS (if any). 3317 o Whether the RS has synchronized time (and thus is able to use the 3318 'exp' claim) or not. 3320 Appendix E. Deployment Examples 3322 There is a large variety of IoT deployments, as is indicated in 3323 Appendix A, and this section highlights a few common variants. This 3324 section is not normative but illustrates how the framework can be 3325 applied. 3327 For each of the deployment variants, there are a number of possible 3328 security setups between clients, resource servers and authorization 3329 servers. The main focus in the following subsections is on how 3330 authorization of a client request for a resource hosted by an RS is 3331 performed. This requires the security of the requests and responses 3332 between the clients and the RS to be considered. 3334 Note: CBOR diagnostic notation is used for examples of requests and 3335 responses. 3337 E.1. Local Token Validation 3339 In this scenario, the case where the resource server is offline is 3340 considered, i.e., it is not connected to the AS at the time of the 3341 access request. This access procedure involves steps A, B, C, and F 3342 of Figure 1. 3344 Since the resource server must be able to verify the access token 3345 locally, self-contained access tokens must be used. 3347 This example shows the interactions between a client, the 3348 authorization server and a temperature sensor acting as a resource 3349 server. Message exchanges A and B are shown in Figure 17. 3351 A: The client first generates a public-private key pair used for 3352 communication security with the RS. 3353 The client sends a CoAP POST request to the token endpoint at the 3354 AS. The security of this request can be transport or application 3355 layer. It is up the the communication security profile to define. 3356 In the example it is assumed that both client and AS have 3357 performed mutual authentication e.g. via DTLS. The request 3358 contains the public key of the client and the Audience parameter 3359 set to "tempSensorInLivingRoom", a value that the temperature 3360 sensor identifies itself with. The AS evaluates the request and 3361 authorizes the client to access the resource. 3362 B: The AS responds with a 2.05 Content response containing the 3363 Access Information, including the access token. The PoP access 3364 token contains the public key of the client, and the Access 3365 Information contains the public key of the RS. For communication 3366 security this example uses DTLS RawPublicKey between the client 3367 and the RS. The issued token will have a short validity time, 3368 i.e., "exp" close to "iat", in order to mitigate attacks using 3369 stolen client credentials. The token includes the claim such as 3370 "scope" with the authorized access that an owner of the 3371 temperature device can enjoy. In this example, the "scope" claim, 3372 issued by the AS, informs the RS that the owner of the token, that 3373 can prove the possession of a key is authorized to make a GET 3374 request against the /temperature resource and a POST request on 3375 the /firmware resource. Note that the syntax and semantics of the 3376 scope claim are application specific. 3377 Note: In this example it is assumed that the client knows what 3378 resource it wants to access, and is therefore able to request 3379 specific audience and scope claims for the access token. 3381 Authorization 3382 Client Server 3383 | | 3384 |<=======>| DTLS Connection Establishment 3385 | | and mutual authentication 3386 | | 3387 A: +-------->| Header: POST (Code=0.02) 3388 | POST | Uri-Path:"token" 3389 | | Content-Format: application/ace+cbor 3390 | | Payload: 3391 | | 3392 B: |<--------+ Header: 2.05 Content 3393 | 2.05 | Content-Format: application/ace+cbor 3394 | | Payload: 3395 | | 3397 Figure 17: Token Request and Response Using Client Credentials. 3399 The information contained in the Request-Payload and the Response- 3400 Payload is shown in Figure 18 Note that the parameter "rs_cnf" from 3401 [I-D.ietf-ace-oauth-params] is used to inform the client about the 3402 resource server's public key. 3404 Request-Payload : 3405 { 3406 "audience" : "tempSensorInLivingRoom", 3407 "client_id" : "myclient", 3408 "req_cnf" : { 3409 "COSE_Key" : { 3410 "kid" : b64'1Bg8vub9tLe1gHMzV76e8', 3411 "kty" : "EC", 3412 "crv" : "P-256", 3413 "x" : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU', 3414 "y" : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0' 3415 } 3416 } 3417 } 3419 Response-Payload : 3420 { 3421 "access_token" : b64'0INDoQEKoQVNKkXfb7xaWqMTf6 ...', 3422 "rs_cnf" : { 3423 "COSE_Key" : { 3424 "kid" : b64'c29tZSBwdWJsaWMga2V5IGlk', 3425 "kty" : "EC", 3426 "crv" : "P-256", 3427 "x" : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4', 3428 "y" : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM' 3429 } 3430 } 3431 } 3433 Figure 18: Request and Response Payload Details. 3435 The content of the access token is shown in Figure 19. 3437 { 3438 "aud" : "tempSensorInLivingRoom", 3439 "iat" : "1563451500", 3440 "exp" : "1563453000", 3441 "scope" : "temperature_g firmware_p", 3442 "cnf" : { 3443 "COSE_Key" : { 3444 "kid" : b64'1Bg8vub9tLe1gHMzV76e8', 3445 "kty" : "EC", 3446 "crv" : "P-256", 3447 "x" : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU', 3448 "y" : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0' 3449 } 3450 } 3451 } 3453 Figure 19: Access Token including Public Key of the Client. 3455 Messages C and F are shown in Figure 20 - Figure 21. 3457 C: The client then sends the PoP access token to the authz-info 3458 endpoint at the RS. This is a plain CoAP POST request, i.e., no 3459 transport or application layer security is used between client and 3460 RS since the token is integrity protected between the AS and RS. 3461 The RS verifies that the PoP access token was created by a known 3462 and trusted AS, that it applies to this RS, and that it is valid. 3463 The RS caches the security context together with authorization 3464 information about this client contained in the PoP access token. 3466 Resource 3467 Client Server 3468 | | 3469 C: +-------->| Header: POST (Code=0.02) 3470 | POST | Uri-Path:"authz-info" 3471 | | Payload: 0INDoQEKoQVN ... 3472 | | 3473 |<--------+ Header: 2.04 Changed 3474 | 2.04 | 3475 | | 3477 Figure 20: Access Token provisioning to RS 3478 The client and the RS runs the DTLS handshake using the raw public 3479 keys established in step B and C. 3480 The client sends a CoAP GET request to /temperature on RS over 3481 DTLS. The RS verifies that the request is authorized, based on 3482 previously established security context. 3484 F: The RS responds over the same DTLS channel with a CoAP 2.05 3485 Content response, containing a resource representation as payload. 3487 Resource 3488 Client Server 3489 | | 3490 |<=======>| DTLS Connection Establishment 3491 | | using Raw Public Keys 3492 | | 3493 +-------->| Header: GET (Code=0.01) 3494 | GET | Uri-Path: "temperature" 3495 | | 3496 | | 3497 | | 3498 F: |<--------+ Header: 2.05 Content 3499 | 2.05 | Payload: 3500 | | 3502 Figure 21: Resource Request and Response protected by DTLS. 3504 E.2. Introspection Aided Token Validation 3506 In this deployment scenario it is assumed that a client is not able 3507 to access the AS at the time of the access request, whereas the RS is 3508 assumed to be connected to the back-end infrastructure. Thus the RS 3509 can make use of token introspection. This access procedure involves 3510 steps A-F of Figure 1, but assumes steps A and B have been carried 3511 out during a phase when the client had connectivity to AS. 3513 Since the client is assumed to be offline, at least for a certain 3514 period of time, a pre-provisioned access token has to be long-lived. 3515 Since the client is constrained, the token will not be self contained 3516 (i.e. not a CWT) but instead just a reference. The resource server 3517 uses its connectivity to learn about the claims associated to the 3518 access token by using introspection, which is shown in the example 3519 below. 3521 In the example interactions between an offline client (key fob), an 3522 RS (online lock), and an AS is shown. It is assumed that there is a 3523 provisioning step where the client has access to the AS. This 3524 corresponds to message exchanges A and B which are shown in 3525 Figure 22. 3527 Authorization consent from the resource owner can be pre-configured, 3528 but it can also be provided via an interactive flow with the resource 3529 owner. An example of this for the key fob case could be that the 3530 resource owner has a connected car, he buys a generic key that he 3531 wants to use with the car. To authorize the key fob he connects it 3532 to his computer that then provides the UI for the device. After that 3533 OAuth 2.0 implicit flow can used to authorize the key for his car at 3534 the the car manufacturers AS. 3536 Note: In this example the client does not know the exact door it will 3537 be used to access since the token request is not send at the time of 3538 access. So the scope and audience parameters are set quite wide to 3539 start with, while tailored values narrowing down the claims to the 3540 specific RS being accessed can be provided to that RS during an 3541 introspection step. 3543 A: The client sends a CoAP POST request to the token endpoint at 3544 AS. The request contains the Audience parameter set to "PACS1337" 3545 (PACS, Physical Access System), a value the that identifies the 3546 physical access control system to which the individual doors are 3547 connected. The AS generates an access token as an opaque string, 3548 which it can match to the specific client and the targeted 3549 audience. It furthermore generates a symmetric proof-of- 3550 possession key. The communication security and authentication 3551 between client and AS is assumed to have been provided at 3552 transport layer (e.g. via DTLS) using a pre-shared security 3553 context (psk, rpk or certificate). 3554 B: The AS responds with a CoAP 2.05 Content response, containing 3555 as playload the Access Information, including the access token and 3556 the symmetric proof-of-possession key. Communication security 3557 between C and RS will be DTLS and PreSharedKey. The PoP key is 3558 used as the PreSharedKey. 3560 Note: In this example we are using a symmetric key for a multi-RS 3561 audience, which is not recommended normally (see Section 6.9). 3562 However in this case the risk is deemed to be acceptable, since all 3563 the doors are part of the same physical access control system, and 3564 therefore the risk of a malicious RS impersonating the client towards 3565 another RS is low. 3567 Authorization 3568 Client Server 3569 | | 3570 |<=======>| DTLS Connection Establishment 3571 | | and mutual authentication 3572 | | 3573 A: +-------->| Header: POST (Code=0.02) 3574 | POST | Uri-Path:"token" 3575 | | Content-Format: application/ace+cbor 3576 | | Payload: 3577 | | 3578 B: |<--------+ Header: 2.05 Content 3579 | | Content-Format: application/ace+cbor 3580 | 2.05 | Payload: 3581 | | 3583 Figure 22: Token Request and Response using Client Credentials. 3585 The information contained in the Request-Payload and the Response- 3586 Payload is shown in Figure 23. 3588 Request-Payload: 3589 { 3590 "client_id" : "keyfob", 3591 "audience" : "PACS1337" 3592 } 3594 Response-Payload: 3595 { 3596 "access_token" : b64'VGVzdCB0b2tlbg==', 3597 "cnf" : { 3598 "COSE_Key" : { 3599 "kid" : b64'c29tZSBwdWJsaWMga2V5IGlk', 3600 "kty" : "oct", 3601 "alg" : "HS256", 3602 "k": b64'ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE' 3603 } 3604 } 3605 } 3607 Figure 23: Request and Response Payload for C offline 3609 The access token in this case is just an opaque byte string 3610 referencing the authorization information at the AS. 3612 C: Next, the client POSTs the access token to the authz-info 3613 endpoint in the RS. This is a plain CoAP request, i.e., no DTLS 3614 between client and RS. Since the token is an opaque string, the 3615 RS cannot verify it on its own, and thus defers to respond the 3616 client with a status code until after step E. 3617 D: The RS sends the token to the introspection endpoint on the AS 3618 using a CoAP POST request. In this example RS and AS are assumed 3619 to have performed mutual authentication using a pre shared 3620 security context (psk, rpk or certificate) with the RS acting as 3621 DTLS client. 3622 E: The AS provides the introspection response (2.05 Content) 3623 containing parameters about the token. This includes the 3624 confirmation key (cnf) parameter that allows the RS to verify the 3625 client's proof of possession in step F. Note that our example in 3626 Figure 25 assumes a pre-established key (e.g. one used by the 3627 client and the RS for a previous token) that is now only 3628 referenced by its key-identifier 'kid'. 3629 After receiving message E, the RS responds to the client's POST in 3630 step C with the CoAP response code 2.01 (Created). 3632 Resource 3633 Client Server 3634 | | 3635 C: +-------->| Header: POST (T=CON, Code=0.02) 3636 | POST | Uri-Path:"authz-info" 3637 | | Payload: b64'VGVzdCB0b2tlbg==' 3638 | | 3639 | | Authorization 3640 | | Server 3641 | | | 3642 | D: +--------->| Header: POST (Code=0.02) 3643 | | POST | Uri-Path: "introspect" 3644 | | | Content-Format: "application/ace+cbor" 3645 | | | Payload: 3646 | | | 3647 | E: |<---------+ Header: 2.05 Content 3648 | | 2.05 | Content-Format: "application/ace+cbor" 3649 | | | Payload: 3650 | | | 3651 | | 3652 |<--------+ Header: 2.01 Created 3653 | 2.01 | 3654 | | 3656 Figure 24: Token Introspection for C offline 3657 The information contained in the Request-Payload and the Response- 3658 Payload is shown in Figure 25. 3660 Request-Payload: 3661 { 3662 "token" : b64'VGVzdCB0b2tlbg==', 3663 "client_id" : "FrontDoor", 3664 } 3666 Response-Payload: 3667 { 3668 "active" : true, 3669 "aud" : "lockOfDoor4711", 3670 "scope" : "open, close", 3671 "iat" : 1563454000, 3672 "cnf" : { 3673 "kid" : b64'c29tZSBwdWJsaWMga2V5IGlk' 3674 } 3675 } 3677 Figure 25: Request and Response Payload for Introspection 3679 The client uses the symmetric PoP key to establish a DTLS 3680 PreSharedKey secure connection to the RS. The CoAP request PUT is 3681 sent to the uri-path /state on the RS, changing the state of the 3682 door to locked. 3683 F: The RS responds with a appropriate over the secure DTLS 3684 channel. 3686 Resource 3687 Client Server 3688 | | 3689 |<=======>| DTLS Connection Establishment 3690 | | using Pre Shared Key 3691 | | 3692 +-------->| Header: PUT (Code=0.03) 3693 | PUT | Uri-Path: "state" 3694 | | Payload: 3695 | | 3696 F: |<--------+ Header: 2.04 Changed 3697 | 2.04 | Payload: 3698 | | 3700 Figure 26: Resource request and response protected by OSCORE 3702 Appendix F. Document Updates 3704 RFC EDITOR: PLEASE REMOVE THIS SECTION. 3706 F.1. Version -21 to 22 3708 o Provided section numbers in references to OAuth RFC. 3709 o Updated IANA mapping registries to only use "Private Use" and 3710 "Expert Review". 3711 o Made error messages optional for RS at token submission since it 3712 may not be able to send them depending on the profile. 3713 o Corrected errors in examples. 3715 F.2. Version -20 to 21 3717 o Added text about expiration of RS keys. 3719 F.3. Version -19 to 20 3721 o Replaced "req_aud" with "audience" from the OAuth token exchange 3722 draft. 3723 o Updated examples to remove unnecessary elements. 3725 F.4. Version -18 to -19 3727 o Added definition of "Authorization Information". 3728 o Explicitly state that ACE allows encoding refresh tokens in binary 3729 format in addition to strings. 3730 o Renamed "AS Information" to "AS Request Creation Hints" and added 3731 the possibility to specify req_aud and scope as hints. 3732 o Added the "kid" parameter to AS Request Creation Hints. 3733 o Added security considerations about the integrity protection of 3734 tokens with multi-RS audiences. 3735 o Renamed IANA registries mapping OAuth parameters to reflect the 3736 mapped registry. 3737 o Added JWT claim names to CWT claim registrations. 3738 o Added expert review instructions. 3739 o Updated references to TLS from 1.2 to 1.3. 3741 F.5. Version -17 to -18 3743 o Added OSCORE options in examples involving OSCORE. 3744 o Removed requirement for the client to send application/cwt, since 3745 the client has no way to know. 3746 o Clarified verification of tokens by the RS. 3747 o Added exi claim CWT registration. 3749 F.6. Version -16 to -17 3751 o Added references to (D)TLS 1.3. 3752 o Added requirement that responses are bound to requests. 3754 o Specify that grant_type is OPTIONAL in C2AS requests (as opposed 3755 to REQUIRED in OAuth). 3756 o Replaced examples with hypothetical COSE profile with OSCORE. 3757 o Added requirement for content type application/ace+cbor in error 3758 responses for token and introspection requests and responses. 3759 o Reworked abbreviation space for claims, request and response 3760 parameters. 3761 o Added text that the RS may indicate that it is busy at the authz- 3762 info resource. 3763 o Added section that specifies how the RS verifies an access token. 3764 o Added section on the protection of the authz-info endpoint. 3765 o Removed the expiration mechanism based on sequence numbers. 3766 o Added reference to RFC7662 security considerations. 3767 o Added considerations on minimal security requirements for 3768 communication. 3769 o Added security considerations on unprotected information sent to 3770 authz-info and in the error responses. 3772 F.7. Version -15 to -16 3774 o Added text the RS using RFC6750 error codes. 3775 o Defined an error code for incompatible token request parameters. 3776 o Removed references to the actors draft. 3777 o Fixed errors in examples. 3779 F.8. Version -14 to -15 3781 o Added text about refresh tokens. 3782 o Added text about protection of credentials. 3783 o Rephrased introspection so that other entities than RS can do it. 3784 o Editorial improvements. 3786 F.9. Version -13 to -14 3788 o Split out the 'aud', 'cnf' and 'rs_cnf' parameters to 3789 [I-D.ietf-ace-oauth-params] 3790 o Introduced the "application/ace+cbor" Content-Type. 3791 o Added claim registrations from 'profile' and 'rs_cnf'. 3792 o Added note on schema part of AS Information Section 5.3 3793 o Realigned the parameter abbreviations to push rarely used ones to 3794 the 2-byte encoding size of CBOR integers. 3796 F.10. Version -12 to -13 3798 o Changed "Resource Information" to "Access Information" to avoid 3799 confusion. 3800 o Clarified section about AS discovery. 3801 o Editorial changes 3803 F.11. Version -11 to -12 3805 o Moved the Request error handling to a section of its own. 3806 o Require the use of the abbreviation for profile identifiers. 3807 o Added rs_cnf parameter in the introspection response, to inform 3808 RS' with several RPKs on which key to use. 3809 o Allowed use of rs_cnf as claim in the access token in order to 3810 inform an RS with several RPKs on which key to use. 3811 o Clarified that profiles must specify if/how error responses are 3812 protected. 3813 o Fixed label number range to align with COSE/CWT. 3814 o Clarified the requirements language in order to allow profiles to 3815 specify other payload formats than CBOR if they do not use CoAP. 3817 F.12. Version -10 to -11 3819 o Fixed some CBOR data type errors. 3820 o Updated boilerplate text 3822 F.13. Version -09 to -10 3824 o Removed CBOR major type numbers. 3825 o Removed the client token design. 3826 o Rephrased to clarify that other protocols than CoAP can be used. 3827 o Clarifications regarding the use of HTTP 3829 F.14. Version -08 to -09 3831 o Allowed scope to be byte strings. 3832 o Defined default names for endpoints. 3833 o Refactored the IANA section for briefness and consistency. 3834 o Refactored tables that define IANA registry contents for 3835 consistency. 3836 o Created IANA registry for CBOR mappings of error codes, grant 3837 types and Authorization Server Information. 3838 o Added references to other document sections defining IANA entries 3839 in the IANA section. 3841 F.15. Version -07 to -08 3843 o Moved AS discovery from the DTLS profile to the framework, see 3844 Section 5.1. 3845 o Made the use of CBOR mandatory. If you use JSON you can use 3846 vanilla OAuth. 3847 o Made it mandatory for profiles to specify C-AS security and RS-AS 3848 security (the latter only if introspection is supported). 3849 o Made the use of CBOR abbreviations mandatory. 3851 o Added text to clarify the use of token references as an 3852 alternative to CWTs. 3853 o Added text to clarify that introspection must not be delayed, in 3854 case the RS has to return a client token. 3855 o Added security considerations about leakage through unprotected AS 3856 discovery information, combining profiles and leakage through 3857 error responses. 3858 o Added privacy considerations about leakage through unprotected AS 3859 discovery. 3860 o Added text that clarifies that introspection is optional. 3861 o Made profile parameter optional since it can be implicit. 3862 o Clarified that CoAP is not mandatory and other protocols can be 3863 used. 3864 o Clarified the design justification for specific features of the 3865 framework in appendix A. 3866 o Clarified appendix E.2. 3867 o Removed specification of the "cnf" claim for CBOR/COSE, and 3868 replaced with references to [RFC8747] 3870 F.16. Version -06 to -07 3872 o Various clarifications added. 3873 o Fixed erroneous author email. 3875 F.17. Version -05 to -06 3877 o Moved sections that define the ACE framework into a subsection of 3878 the framework Section 5. 3879 o Split section on client credentials and grant into two separate 3880 sections, Section 5.4, and Section 5.5. 3881 o Added Section 5.6 on AS authentication. 3882 o Added Section 5.7 on the Authorization endpoint. 3884 F.18. Version -04 to -05 3886 o Added RFC 2119 language to the specification of the required 3887 behavior of profile specifications. 3888 o Added Section 5.5 on the relation to the OAuth2 grant types. 3889 o Added CBOR abbreviations for error and the error codes defined in 3890 OAuth2. 3891 o Added clarification about token expiration and long-running 3892 requests in Section 5.10.3 3893 o Added security considerations about tokens with symmetric PoP keys 3894 valid for more than one RS. 3895 o Added privacy considerations section. 3896 o Added IANA registry mapping the confirmation types from RFC 7800 3897 to equivalent COSE types. 3899 o Added appendix D, describing assumptions about what the AS knows 3900 about the client and the RS. 3902 F.19. Version -03 to -04 3904 o Added a description of the terms "framework" and "profiles" as 3905 used in this document. 3906 o Clarified protection of access tokens in section 3.1. 3907 o Clarified uses of the "cnf" parameter in section 6.4.5. 3908 o Clarified intended use of Client Token in section 7.4. 3910 F.20. Version -02 to -03 3912 o Removed references to draft-ietf-oauth-pop-key-distribution since 3913 the status of this draft is unclear. 3914 o Copied and adapted security considerations from draft-ietf-oauth- 3915 pop-key-distribution. 3916 o Renamed "client information" to "RS information" since it is 3917 information about the RS. 3918 o Clarified the requirements on profiles of this framework. 3919 o Clarified the token endpoint protocol and removed negotiation of 3920 "profile" and "alg" (section 6). 3921 o Renumbered the abbreviations for claims and parameters to get a 3922 consistent numbering across different endpoints. 3923 o Clarified the introspection endpoint. 3924 o Renamed token, introspection and authz-info to "endpoint" instead 3925 of "resource" to mirror the OAuth 2.0 terminology. 3926 o Updated the examples in the appendices. 3928 F.21. Version -01 to -02 3930 o Restructured to remove communication security parts. These shall 3931 now be defined in profiles. 3932 o Restructured section 5 to create new sections on the OAuth 3933 endpoints token, introspection and authz-info. 3934 o Pulled in material from draft-ietf-oauth-pop-key-distribution in 3935 order to define proof-of-possession key distribution. 3936 o Introduced the "cnf" parameter as defined in RFC7800 to reference 3937 or transport keys used for proof of possession. 3938 o Introduced the "client-token" to transport client information from 3939 the AS to the client via the RS in conjunction with introspection. 3940 o Expanded the IANA section to define parameters for token request, 3941 introspection and CWT claims. 3942 o Moved deployment scenarios to the appendix as examples. 3944 F.22. Version -00 to -01 3946 o Changed 5.1. from "Communication Security Protocol" to "Client 3947 Information". 3948 o Major rewrite of 5.1 to clarify the information exchanged between 3949 C and AS in the PoP access token request profile for IoT. 3951 * Allow the client to indicate preferences for the communication 3952 security protocol. 3953 * Defined the term "Client Information" for the additional 3954 information returned to the client in addition to the access 3955 token. 3956 * Require that the messages between AS and client are secured, 3957 either with (D)TLS or with COSE_Encrypted wrappers. 3958 * Removed dependency on OSCOAP and added generic text about 3959 object security instead. 3960 * Defined the "rpk" parameter in the client information to 3961 transmit the raw public key of the RS from AS to client. 3962 * (D)TLS MUST use the PoP key in the handshake (either as PSK or 3963 as client RPK with client authentication). 3964 * Defined the use of x5c, x5t and x5tS256 parameters when a 3965 client certificate is used for proof of possession. 3966 * Defined "tktn" parameter for signaling for how to transfer the 3967 access token. 3968 o Added 5.2. the CoAP Access-Token option for transferring access 3969 tokens in messages that do not have payload. 3970 o 5.3.2. Defined success and error responses from the RS when 3971 receiving an access token. 3972 o 5.6.:Added section giving guidance on how to handle token 3973 expiration in the absence of reliable time. 3974 o Appendix B Added list of roles and responsibilities for C, AS and 3975 RS. 3977 Authors' Addresses 3979 Ludwig Seitz 3980 Combitech 3981 Djaeknegatan 31 3982 Malmoe 211 35 3983 Sweden 3985 Email: ludwig.seitz@combitech.se 3986 Goeran Selander 3987 Ericsson 3988 Faroegatan 6 3989 Kista 164 80 3990 Sweden 3992 Email: goran.selander@ericsson.com 3994 Erik Wahlstroem 3995 Sweden 3997 Email: erik@wahlstromstekniska.se 3999 Samuel Erdtman 4000 Spotify AB 4001 Birger Jarlsgatan 61, 4tr 4002 Stockholm 113 56 4003 Sweden 4005 Email: erdtman@spotify.com 4007 Hannes Tschofenig 4008 Arm Ltd. 4009 Absam 6067 4010 Austria 4012 Email: Hannes.Tschofenig@arm.com