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Nottingham 3 Internet-Draft Fastly 4 Intended status: Standards Track P. Sikora 5 Expires: November 3, 2019 Google 6 May 2, 2019 8 The Proxy-Status HTTP Header Field 9 draft-ietf-httpbis-proxy-status-00 11 Abstract 13 This document defines the Proxy-Status HTTP header field to convey 14 the details of errors generated by HTTP intermediaries. 16 Note to Readers 18 _RFC EDITOR: please remove this section before publication_ 20 Discussion of this draft takes place on the HTTP working group 21 mailing list (ietf-http-wg@w3.org), which is archived at 22 https://lists.w3.org/Archives/Public/ietf-http-wg/ [1]. 24 Working Group information can be found at https://httpwg.org/ [2]; 25 source code and issues list for this draft can be found at 26 https://github.com/httpwg/http-extensions/labels/proxy-status [3]. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on November 3, 2019. 45 Copyright Notice 47 Copyright (c) 2019 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 63 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3 64 2. The Proxy-Status HTTP Header Field . . . . . . . . . . . . . 4 65 2.1. Generic Proxy Status Parameters . . . . . . . . . . . . . 5 66 3. Proxy Status Types . . . . . . . . . . . . . . . . . . . . . 6 67 3.1. DNS Timeout . . . . . . . . . . . . . . . . . . . . . . . 6 68 3.2. DNS Error . . . . . . . . . . . . . . . . . . . . . . . . 6 69 3.3. Destination Not Found . . . . . . . . . . . . . . . . . . 6 70 3.4. Destination Unavailable . . . . . . . . . . . . . . . . . 7 71 3.5. Destination IP Prohibited . . . . . . . . . . . . . . . . 7 72 3.6. Destination IP Unroutable . . . . . . . . . . . . . . . . 7 73 3.7. Connection Refused . . . . . . . . . . . . . . . . . . . 7 74 3.8. Connection Terminated . . . . . . . . . . . . . . . . . . 8 75 3.9. Connection Timeout . . . . . . . . . . . . . . . . . . . 8 76 3.10. Connection Read Timeout . . . . . . . . . . . . . . . . . 8 77 3.11. Connection Write Timeout . . . . . . . . . . . . . . . . 8 78 3.12. Connection Limit Reached . . . . . . . . . . . . . . . . 9 79 3.13. HTTP Response Status . . . . . . . . . . . . . . . . . . 9 80 3.14. HTTP Incomplete Response . . . . . . . . . . . . . . . . 9 81 3.15. HTTP Protocol Error . . . . . . . . . . . . . . . . . . . 9 82 3.16. HTTP Response Header Block Too Large . . . . . . . . . . 10 83 3.17. HTTP Response Header Too Large . . . . . . . . . . . . . 10 84 3.18. HTTP Response Body Too Large . . . . . . . . . . . . . . 10 85 3.19. HTTP Response Transfer-Coding Error . . . . . . . . . . . 11 86 3.20. HTTP Response Content-Coding Error . . . . . . . . . . . 11 87 3.21. HTTP Response Timeout . . . . . . . . . . . . . . . . . . 11 88 3.22. TLS Handshake Error . . . . . . . . . . . . . . . . . . . 12 89 3.23. TLS Untrusted Peer Certificate . . . . . . . . . . . . . 12 90 3.24. TLS Expired Peer Certificate . . . . . . . . . . . . . . 12 91 3.25. TLS Unexpected Peer Certificate . . . . . . . . . . . . . 12 92 3.26. TLS Unexpected Peer Identity . . . . . . . . . . . . . . 13 93 3.27. TLS Missing Proxy Certificate . . . . . . . . . . . . . . 13 94 3.28. TLS Rejected Proxy Certificate . . . . . . . . . . . . . 13 95 3.29. TLS Error . . . . . . . . . . . . . . . . . . . . . . . . 13 96 3.30. HTTP Request Error . . . . . . . . . . . . . . . . . . . 14 97 3.31. HTTP Request Denied . . . . . . . . . . . . . . . . . . . 14 98 3.32. HTTP Upgrade Failed . . . . . . . . . . . . . . . . . . . 14 99 3.33. Proxy Internal Error . . . . . . . . . . . . . . . . . . 14 100 3.34. Proxy Loop Detected . . . . . . . . . . . . . . . . . . . 15 101 4. Defining New Proxy Status Types . . . . . . . . . . . . . . . 15 102 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 103 6. Security Considerations . . . . . . . . . . . . . . . . . . . 16 104 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 105 7.1. Normative References . . . . . . . . . . . . . . . . . . 16 106 7.2. Informative References . . . . . . . . . . . . . . . . . 17 107 7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 17 108 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 110 1. Introduction 112 HTTP intermediaries - including both forward proxies and gateways 113 (also known as "reverse proxies") - have become an increasingly 114 significant part of HTTP deployments. In particular, reverse proxies 115 and Content Delivery Networks (CDNs) form part of the critical 116 infrastructure of many Web sites. 118 Typically, HTTP intermediaries forward requests towards the origin 119 server and then forward their responses back to clients. However, if 120 an error occurs, the response is generated by the intermediary 121 itself. 123 HTTP accommodates these types of errors with a few status codes; for 124 example, 502 Bad Gateway and 504 Gateway Timeout. However, 125 experience has shown that more information is necessary to aid 126 debugging and communicate what's happened to the client. 128 To address this, Section 2 defines a new HTTP response header field 129 to convey such information, using the Proxy Status Types defined in 130 Section 3. Section 4 explains how to define new Proxy Status Types. 132 1.1. Notational Conventions 134 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 135 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 136 "OPTIONAL" in this document are to be interpreted as described in BCP 137 14 [RFC2119] [RFC8174] when, and only when, they appear in all 138 capitals, as shown here. 140 This specification uses Structured Headers 141 [I-D.ietf-httpbis-header-structure] to specify syntax. The terms sh- 142 param-list, sh-item, sh-string, sh-token and sh-integer refer to the 143 structured types defined therein. 145 Note that in this specification, "proxy" is used to indicate both 146 forward and reverse proxies, otherwise known as gateways. "Next hop" 147 indicates the connection in the direction leading to the origin 148 server for the request. 150 2. The Proxy-Status HTTP Header Field 152 The Proxy-Status HTTP response header field allows an intermediary to 153 indicate the nature and details of an error condition it encounters 154 when servicing a request. 156 It is a Structured Headers [I-D.ietf-httpbis-header-structure] 157 Parameterised List, where each item in the list indicates an error 158 condition. Typically, it will have only one param-item (the error 159 condition that triggered generation of the response it occurs 160 within), but more than one value is not prohibited. 162 Each param-item's primary-id is a Proxy Status Type, a registered 163 value that indicates the nature of the error. 165 Each param-item can have zero to many parameters. Section 2.1 lists 166 parameters that can be used with all Proxy Status Types; individual 167 types can define additional parameters to use with them. All 168 parameters are optional; see Section 6 for their potential security 169 impact. 171 For example: 173 HTTP/1.1 504 Gateway Timeout 174 Proxy-Status: connection_timeout; proxy=SomeCDN; origin=abc; tries=3 176 indicates the specific nature of the timeout as a connect timeout to 177 the origin with the identifier "abc", and that is was generated by 178 the intermediary that identifies itself as "FooCDN." Furthermore, 179 three connection attempts were made. 181 Or: 183 HTTP/1.1 429 Too Many Requests 184 Proxy-Status: http_request_error; proxy=SomeReverseProxy 186 indicates that this 429 Too Many Requests response was generated by 187 the intermediary, not the origin. 189 Each Proxy Status Type has a Recommended HTTP Status Code. When 190 generating a HTTP response containing Proxy-Status, its HTTP status 191 code SHOULD be set to the Recommended HTTP Status Code. However, 192 there may be circumstances (e.g., for backwards compatibility with 193 previous behaviours) when another status code might be used. 195 Section 3 lists the Proxy Status Types defined in this document; new 196 ones can be defined using the procedure outlined in Section 4. 198 Proxy-Status MAY be sent in HTTP trailers, but - as with all trailers 199 - it might be silently discarded along the path to the user agent, 200 this SHOULD NOT be done unless it is not possible to send it in 201 headers. For example, if an intermediary is streaming a response and 202 the upstream connection suddenly terminates, Proxy-Status can be 203 appended to the trailers of the outgoing message (since the headers 204 have already been sent). 206 Note that there are various security considerations for 207 intermediaries using the Proxy-Status header field; see Section 6. 209 Origin servers MUST NOT generate the Proxy-Status header field. 211 2.1. Generic Proxy Status Parameters 213 This section lists parameters that are potentially applicable to most 214 Proxy Status Types. 216 o proxy - a sh-token identifying the HTTP intermediary generating 217 this response. 219 o origin - a sh-token identifying the origin server whose behaviour 220 triggered this response. 222 o protocol - a sh-token indicating the ALPN protocol identifier 223 [RFC7301] used to connect to the next hop. This is only 224 applicable when that connection was actually established. 226 o tries - a sh-integer indicating the number of times that the error 227 has occurred before this response. 229 o details - a sh-string containing additional information not 230 captured anywhere else. This can include implementation-specific 231 or deployment-specific information. 233 3. Proxy Status Types 235 This section lists the Proxy Status Types defined by this document. 236 See Section 4 for information about defining new Proxy Status Types. 238 3.1. DNS Timeout 240 o Name: dns_timeout 242 o Description: The intermediary encountered a timeout when trying to 243 find an IP address for the destination hostname. 245 o Extra Parameters: None. 247 o Recommended HTTP status code: 504 249 3.2. DNS Error 251 o Name: dns_error 253 o Description: The intermediary encountered a DNS error when trying 254 to find an IP address for the destination hostname. 256 o Extra Parameters: 258 * rcode: A sh-string conveying the DNS RCODE that indicates the 259 error type. See [RFC8499], Section 3. 261 o Recommended HTTP status code: 502 263 3.3. Destination Not Found 265 o Name: destination_not_found 267 o Description: The intermediary cannot determine the appropriate 268 destination to use for this request; for example, it may not be 269 configured. Note that this error is specific to gateways, which 270 typically require specific configuration to identify the "backend" 271 server; forward proxies use in-band information to identify the 272 origin server. 274 o Extra Parameters: None. 276 o Recommended HTTP status code: 500 278 3.4. Destination Unavailable 280 o Name: destination_unavailable 282 o Description: The intermediary considers the next hop to be 283 unavailable; e.g., recent attempts to communicate with it may have 284 failed, or a health check may indicate that it is down. 286 o Extra Parameters: 288 o Recommended HTTP status code: 503 290 3.5. Destination IP Prohibited 292 o Name: destination_ip_prohibited 294 o Description: The intermediary is configured to prohibit 295 connections to the destination IP address. 297 o Extra Parameters: None. 299 o Recommended HTTP status code: 502 301 3.6. Destination IP Unroutable 303 o Name: destination_ip_unroutable 305 o Description: The intermediary cannot find a route to the 306 destination IP address. 308 o Extra Parameters: None. 310 o Recommended HTTP status code: 502 312 3.7. Connection Refused 314 o Name: connection_refused 316 o Description: The intermediary's connection to the next hop was 317 refused. 319 o Extra Parameters: None. 321 o Recommended HTTP status code: 502 323 3.8. Connection Terminated 325 o Name: connection_terminated 327 o Description: The intermediary's connection to the next hop was 328 closed before any part of the response was received. If some part 329 was received, see http_response_incomplete. 331 o Extra Parameters: None. 333 o Recommended HTTP status code: 502 335 3.9. Connection Timeout 337 o Name: connection_timeout 339 o Description: The intermediary's attempt to open a connection to 340 the next hop timed out. 342 o Extra Parameters: None. 344 o Recommended HTTP status code: 504 346 3.10. Connection Read Timeout 348 o Name: connection_read_timeout 350 o Description: The intermediary was expecting data on a connection 351 (e.g., part of a response), but did not receive any new data in a 352 configured time limit. 354 o Extra Parameters: None. 356 o Recommended HTTP status code: 504 358 3.11. Connection Write Timeout 360 o Name: connection_write_timeout 362 o Description: The intermediary was attempting to write data to a 363 connection, but was not able to (e.g., because its buffers were 364 full). 366 o Extra Parameters: None. 368 o Recommended HTTP status code: 504 370 3.12. Connection Limit Reached 372 o Name: connnection_limit_reached 374 o Description: The intermediary is configured to limit the number of 375 connections it has to the next hop, and that limit has been 376 passed. 378 o Extra Parameters: None. 380 o Recommended HTTP status code: 382 3.13. HTTP Response Status 384 o Name: http_response_status 386 o Description: The intermediary has received a 4xx or 5xx status 387 code from the next hop and forwarded it to the client. 389 o Extra Parameters: None. 391 o Recommended HTTP status code: 393 3.14. HTTP Incomplete Response 395 o Name: http_response_incomplete 397 o Description: The intermediary received an incomplete response to 398 the request from the next hop. 400 o Extra Parameters: None. 402 o Recommended HTTP status code: 502 404 3.15. HTTP Protocol Error 406 o Name: http_protocol_error 408 o Description: The intermediary encountered a HTTP protocol error 409 when communicating with the next hop. This error should only be 410 used when a more specific one is not defined. 412 o Extra Parameters: 414 * details: a sh-string containing details about the error 415 condition. For example, this might be the HTTP/2 error code or 416 free-form text describing the condition. 418 o Recommended HTTP status code: 502 420 3.16. HTTP Response Header Block Too Large 422 o Name: http_response_header_block_size 424 o Description: The intermediary received a response to the request 425 whose header block was considered too large. 427 o Extra Parameters: 429 * header_block_size: a sh-integer indicating how large the 430 headers received were. Note that they might not be complete; 431 i.e., the intermediary may have discarded or refused additional 432 data. 434 o Recommended HTTP status code: 502 436 3.17. HTTP Response Header Too Large 438 o Name: http_response_header_size 440 o Description: The intermediary received a response to the request 441 containing an individual header line that was considered too 442 large. 444 o Extra Parameters: 446 * header_name: a sh-string indicating the name of the header that 447 triggered the error. 449 o Recommended HTTP status code: 502 451 3.18. HTTP Response Body Too Large 453 o Name: http_response_body_size 455 o Description: The intermediary received a response to the request 456 whose body was considered too large. 458 o Extra Parameters: 460 * body_size: a sh-integer indicating how large the body received 461 was. Note that it may not have been complete; i.e., the 462 intermediary may have discarded or refused additional data. 464 o Recommended HTTP status code: 502 466 3.19. HTTP Response Transfer-Coding Error 468 o Name: http_response_transfer_coding 470 o Description: The intermediary encountered an error decoding the 471 transfer-coding of the response. 473 o Extra Parameters: 475 * coding: a sh-token containing the specific coding that caused 476 the error. 478 * details: a sh-string containing details about the error 479 condition. 481 o Recommended HTTP status code: 502 483 3.20. HTTP Response Content-Coding Error 485 o Name: http_response_content_coding 487 o Description: The intermediary encountered an error decoding the 488 content-coding of the response. 490 o Extra Parameters: 492 * coding: a sh-token containing the specific coding that caused 493 the error. 495 * details: a sh-string containing details about the error 496 condition. 498 o Recommended HTTP status code: 502 500 3.21. HTTP Response Timeout 502 o Name: http_response_timeout 504 o Description: The intermediary reached a configured time limit 505 waiting for the complete response. 507 o Extra Parameters: None. 509 o Recommended HTTP status code: 504 511 3.22. TLS Handshake Error 513 o Name: tls_handshake_error 515 o Description: The intermediary encountered an error during TLS 516 handshake with the next hop. 518 o Extra Parameters: 520 * alert_message: a sh-token containing the applicable description 521 string from the TLS Alerts registry. 523 o Recommended HTTP status code: 502 525 3.23. TLS Untrusted Peer Certificate 527 o Name: tls_untrusted_peer_certificate 529 o Description: The intermediary received untrusted peer certificate 530 during TLS handshake with the next hop. 532 o Extra Parameters: None. 534 o Recommended HTTP status code: 502 536 3.24. TLS Expired Peer Certificate 538 o Name: tls_expired_peer_certificate 540 o Description: The intermediary received expired peer certificate 541 during TLS handshake with the next hop. 543 o Extra Parameters: None. 545 o Recommended HTTP status code: 502 547 3.25. TLS Unexpected Peer Certificate 549 o Name: tls_unexpected_peer_certificate 551 o Description: The intermediary received unexpected peer certificate 552 (e.g., SPKI doesn't match) during TLS handshake with the next hop. 554 o Extra Parameters: 556 * details: a sh-string containing the checksum or SPKI of the 557 certificate received from the next hop. 559 o Recommended HTTP status code: 502 561 3.26. TLS Unexpected Peer Identity 563 o Name: tls_unexpected_peer_identity 565 o Description: The intermediary received peer certificate with 566 unexpected identity (e.g., Subject Alternative Name doesn't match) 567 during TLS handshake with the next hop. 569 o Extra Parameters: 571 * details: a sh-string containing the identity of the next hop. 573 o Recommended HTTP status code: 502 575 3.27. TLS Missing Proxy Certificate 577 o Name: tls_missing_proxy_certificate 579 o Description: The next hop requested client certificate from the 580 intermediary during TLS handshake, but it wasn't configured with 581 one. 583 o Extra Parameters: None. 585 o Recommended HTTP status code: 500 587 3.28. TLS Rejected Proxy Certificate 589 o Name: tls_rejected_proxy_certificate 591 o Description: The next hop rejected client certificate provided by 592 the intermediary during TLS handshake. 594 o Extra Parameters: None. 596 o Recommended HTTP status code: 500 598 3.29. TLS Error 600 o Name: tls_error 602 o Description: The intermediary encountered a TLS error when 603 communicating with the next hop. 605 o Extra Parameters: 607 * alert_message: a sh-token containing the applicable description 608 string from the TLS Alerts registry. 610 o Recommended HTTP status code: 502 612 3.30. HTTP Request Error 614 o Name: http_request_error 616 o Description: The intermediary is generating a client (4xx) 617 response on the origin's behalf. Applicable status codes include 618 (but are not limited to) 400, 403, 405, 406, 408, 411, 413, 414, 619 415, 416, 417, 429. This proxy status type helps distinguish 620 between responses generated by intermediaries from those generated 621 by the origin. 623 o Extra Parameters: None. 625 o Recommended HTTP status code: The applicable 4xx status code 627 3.31. HTTP Request Denied 629 o Name: http_request_denied 631 o Description: The intermediary rejected HTTP request based on its 632 configuration and/or policy settings. The request wasn't 633 forwarded to the next hop. 635 o Extra Parameters: None. 637 o Recommended HTTP status code: 400 639 3.32. HTTP Upgrade Failed 641 o Name: http_upgrade_failed 643 o Description: The HTTP Upgrade between the intermediary and the 644 next hop failed. 646 o Extra Parameters: None. 648 o Recommended HTTP status code: 502 650 3.33. Proxy Internal Error 652 o Name: proxy_internal_error 653 o Description: The intermediary encountered an internal error 654 unrelated to the origin. 656 o Extra Parameters: 658 * details: a sh-string containing details about the error 659 condition. 661 o Recommended HTTP status code: 500 663 3.34. Proxy Loop Detected 665 o Name: proxy_loop_detected 667 o Description: The intermediary tried to forward the request to 668 itself, or a loop has been detected using different means (e.g. 669 [I-D.ietf-httpbis-cdn-loop]). 671 o Extra Parameters: None. 673 o Recommended HTTP status code: 502 675 4. Defining New Proxy Status Types 677 New Proxy Status Types can be defined by registering them in the HTTP 678 Proxy Status Types registry. 680 Registration requests are reviewed and approved by a Designated 681 Expert, as per [RFC8126], Section 4.5. A specification document is 682 appreciated, but not required. 684 The Expert(s) should consider the following factors when evaluating 685 requests: 687 o Community feedback 689 o If the value is sufficiently well-defined 691 o If the value is generic; vendor-specific, application-specific and 692 deployment-specific values are discouraged 694 Registration requests should use the following template: 696 o Name: [a name for the Proxy Status Type that is allowable as a sh- 697 param-list key] 699 o Description: [a description of the conditions that generate the 700 Proxy Status Types] 702 o Extra Parameters: [zero or more optional parameters, typed using 703 one of the types available in sh-item] 705 o Recommended HTTP status code: [the appropriate HTTP status code 706 for this entry] 708 See the registry at https://iana.org/assignments/http-proxy-statuses 709 [4] for details on where to send registration requests. 711 5. IANA Considerations 713 Upon publication, please create the HTTP Proxy Status Types registry 714 at https://iana.org/assignments/http-proxy-statuses [5] and populate 715 it with the types defined in Section 3; see Section 4 for its 716 associated procedures. 718 6. Security Considerations 720 One of the primary security concerns when using Proxy-Status is 721 leaking information that might aid an attacker. 723 As a result, care needs to be taken when deciding to generate a 724 Proxy-Status header. Note that intermediaries are not required to 725 generate a Proxy-Status header field in any response, and can 726 conditionally generate them based upon request attributes (e.g., 727 authentication tokens, IP address). 729 Likewise, generation of all parameters is optional. 731 Special care needs to be taken in generating proxy and origin 732 parameters, as they can expose information about the intermediary's 733 configuration and back-end topology. 735 7. References 737 7.1. Normative References 739 [I-D.ietf-httpbis-header-structure] 740 Nottingham, M. and P. Kamp, "Structured Headers for HTTP", 741 draft-ietf-httpbis-header-structure-09 (work in progress), 742 December 2018. 744 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 745 Requirement Levels", BCP 14, RFC 2119, 746 DOI 10.17487/RFC2119, March 1997, 747 . 749 [RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan, 750 "Transport Layer Security (TLS) Application-Layer Protocol 751 Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, 752 July 2014, . 754 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 755 Writing an IANA Considerations Section in RFCs", BCP 26, 756 RFC 8126, DOI 10.17487/RFC8126, June 2017, 757 . 759 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 760 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 761 May 2017, . 763 [RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS 764 Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, 765 January 2019, . 767 7.2. Informative References 769 [I-D.ietf-httpbis-cdn-loop] 770 Ludin, S., Nottingham, M., and N. Sullivan, "CDN Loop 771 Detection", draft-ietf-httpbis-cdn-loop-02 (work in 772 progress), February 2019. 774 7.3. URIs 776 [1] https://lists.w3.org/Archives/Public/ietf-http-wg/ 778 [2] https://httpwg.org/ 780 [3] https://github.com/httpwg/http-extensions/labels/proxy-status 782 [4] https://iana.org/assignments/http-proxy-statuses 784 [5] https://iana.org/assignments/http-proxy-statuses 786 Authors' Addresses 788 Mark Nottingham 789 Fastly 791 Email: mnot@mnot.net 792 URI: https://www.mnot.net/ 793 Piotr Sikora 794 Google 796 Email: piotrsikora@google.com