idnits 2.17.1 draft-young-md-query-14.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (January 12, 2021) is 1171 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- ** Obsolete normative reference: RFC 7230 (Obsoleted by RFC 9110, RFC 9112) ** Obsolete normative reference: RFC 7231 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 7232 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 7234 (Obsoleted by RFC 9111) ** Obsolete normative reference: RFC 7235 (Obsoleted by RFC 9110) -- Obsolete informational reference (is this intentional?): RFC 4844 (Obsoleted by RFC 8729) Summary: 5 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group I. Young, Ed. 3 Internet-Draft Independent 4 Intended status: Informational January 12, 2021 5 Expires: July 16, 2021 7 Metadata Query Protocol 8 draft-young-md-query-14 10 Abstract 12 This document defines a simple protocol for retrieving metadata about 13 named entities, or named collections of entities. The goal of the 14 protocol is to profile various aspects of HTTP to allow requesters to 15 rely on certain, rigorously defined, behaviour. 17 This document is a product of the Research and Education Federations 18 (REFEDS) Working Group process. 20 Editorial Note (To be removed by RFC Editor before publication) 22 Discussion of this draft takes place on the MDX mailing list 23 (mdx@lists.iay.org.uk), which is accessed from [MDX.list]. 25 XML versions, latest edits and the issues list for this document are 26 available from [md-query]. 28 The changes in this draft are summarized in Appendix A.15. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on July 16, 2021. 47 Copyright Notice 49 Copyright (c) 2021 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. 59 Table of Contents 61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 62 1.1. Notation and Conventions . . . . . . . . . . . . . . . . 4 63 1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 64 2. Protocol Transport . . . . . . . . . . . . . . . . . . . . . 4 65 2.1. Transport Protocol . . . . . . . . . . . . . . . . . . . 4 66 2.2. HTTP Version . . . . . . . . . . . . . . . . . . . . . . 4 67 2.3. HTTP Method . . . . . . . . . . . . . . . . . . . . . . . 5 68 2.4. Request Headers . . . . . . . . . . . . . . . . . . . . . 5 69 2.5. Response Headers . . . . . . . . . . . . . . . . . . . . 5 70 2.6. Status Codes . . . . . . . . . . . . . . . . . . . . . . 6 71 2.7. Base URL . . . . . . . . . . . . . . . . . . . . . . . . 6 72 2.8. Content Negotiation . . . . . . . . . . . . . . . . . . . 7 73 3. Metadata Query Protocol . . . . . . . . . . . . . . . . . . . 7 74 3.1. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 7 75 3.2. Protocol . . . . . . . . . . . . . . . . . . . . . . . . 7 76 3.2.1. Request by Identifier . . . . . . . . . . . . . . . . 7 77 3.2.2. Request All Entities . . . . . . . . . . . . . . . . 8 78 3.2.3. Response . . . . . . . . . . . . . . . . . . . . . . 8 79 3.2.4. Example Request and Response . . . . . . . . . . . . 9 80 4. Efficient Retrieval and Caching . . . . . . . . . . . . . . . 9 81 4.1. Conditional Retrieval . . . . . . . . . . . . . . . . . . 9 82 4.2. Content Caching . . . . . . . . . . . . . . . . . . . . . 9 83 4.3. Content Compression . . . . . . . . . . . . . . . . . . . 10 84 5. Protocol Extension Points . . . . . . . . . . . . . . . . . . 10 85 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 86 6.1. Integrity . . . . . . . . . . . . . . . . . . . . . . . . 10 87 6.2. Confidentiality . . . . . . . . . . . . . . . . . . . . . 10 88 6.3. Authentication . . . . . . . . . . . . . . . . . . . . . 10 89 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 90 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 91 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 92 9.1. Normative References . . . . . . . . . . . . . . . . . . 11 93 9.2. Informative References . . . . . . . . . . . . . . . . . 12 94 Appendix A. Change Log (to be removed by RFC Editor before 95 publication) . . . . . . . . . . . . . . . . . . . . 14 96 A.1. Since draft-lajoie-md-query-01 . . . . . . . . . . . . . 14 97 A.2. Since draft-young-md-query-00 . . . . . . . . . . . . . . 14 98 A.3. Since draft-young-md-query-01 . . . . . . . . . . . . . . 15 99 A.4. Since draft-young-md-query-02 . . . . . . . . . . . . . . 15 100 A.5. Since draft-young-md-query-03 . . . . . . . . . . . . . . 15 101 A.6. Since draft-young-md-query-04 . . . . . . . . . . . . . . 15 102 A.7. Since draft-young-md-query-05 . . . . . . . . . . . . . . 16 103 A.8. Since draft-young-md-query-06 . . . . . . . . . . . . . . 16 104 A.9. Since draft-young-md-query-07 . . . . . . . . . . . . . . 16 105 A.10. Since draft-young-md-query-08 . . . . . . . . . . . . . . 16 106 A.11. Since draft-young-md-query-09 . . . . . . . . . . . . . . 16 107 A.12. Since draft-young-md-query-10 . . . . . . . . . . . . . . 16 108 A.13. Since draft-young-md-query-11 . . . . . . . . . . . . . . 16 109 A.14. Since draft-young-md-query-12 . . . . . . . . . . . . . . 17 110 A.15. Since draft-young-md-query-13 . . . . . . . . . . . . . . 17 111 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17 113 1. Introduction 115 Many clients of web-based services are capable of consuming 116 descriptive metadata about a service in order to customize or obtain 117 information about the client's connection parameters. While the form 118 of the metadata (e.g., JSON, XML) and content varies between services 119 this document specifies a set of semantics for HTTP ([RFC7230] et 120 seq.) that allow clients to rely on certain behavior. The defined 121 behavior is meant to make it easy for clients to perform queries, to 122 be efficient for both requesters and responders, and to allow the 123 responder to scale in various ways. 125 The Research and Education Federations group ([REFEDS]) is the voice 126 that articulates the mutual needs of research and education identity 127 federations worldwide. It aims to represent the requirements of 128 research and education in the ever-growing space of access and 129 identity management. 131 From time to time REFEDS will wish to publish a document in the 132 Internet RFC series. Such documents will be published as part of the 133 RFC Independent Submission Stream [RFC4844]; however the REFEDS 134 working group sign-off process will have been followed for these 135 documents, as described in the REFEDS Participant's Agreement 136 [REFEDS.agreement]. 138 This document is a product of the REFEDS Working Group process. 140 1.1. Notation and Conventions 142 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 143 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 144 "OPTIONAL" in this document are to be interpreted as described in 145 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 146 capitals, as shown here. 148 This document makes use of the Augmented BNF metalanguage defined in 149 [STD68]. 151 1.2. Terminology 153 entity: A single logical construct for which metadata may be 154 asserted. Generally this is a network accessible service. 156 metadata: A machine readable description of certain entity 157 characteristics. Generally metadata provides information such as 158 end point references, service contact information, etc. 160 2. Protocol Transport 162 The metadata query protocol seeks to fully employ the features of the 163 HTTP protocol. Additionally this specification makes mandatory some 164 optional HTTP features. 166 2.1. Transport Protocol 168 The metadata query protocol makes use of the HTTP protocol 169 ([RFC7230]) to transmit requests and responses. The underlying HTTP 170 connection MAY make use of any appropriate transport protocol. In 171 particular, the HTTP connection MAY make use of either TCP or TLS at 172 the transport layer. See the Security Considerations section for 173 guidance in choosing an appropriate transport protocol. 175 2.2. HTTP Version 177 Requests from clients MUST NOT use an HTTP version prior to version 178 1.1. Responders MUST reply to such requests using status code 505, 179 "HTTP Version Not Supported". 181 Protocol responders MUST support requests using HTTP version 1.1, and 182 MAY support later versions. 184 2.3. HTTP Method 186 All metadata query requests MUST use the GET method. 188 2.4. Request Headers 190 All metadata query requests MUST include the following HTTP headers: 192 Accept - this header MUST contain the content-type identifying the 193 type, or form, of metadata to be retrieved. See section 5.3.2 of 194 [RFC7231]. 196 All metadata query requests SHOULD include the following HTTP 197 headers: 199 Accept-Charset, see section 5.3.3 of [RFC7231] 201 Accept-Encoding, see section 5.3.4 of [RFC7231] 203 A metadata request to the same URL, after an initial request, MUST 204 include the following header: 206 If-None-Match, see section 3.2 of [RFC7232]. 208 2.5. Response Headers 210 All successful metadata query responses (even those that return no 211 results) MUST include the following headers: 213 Content-Encoding - required if, and only if, content is 214 compressed. See section 3.1.2.2 of [RFC7231]. 216 Content-Type, see section 3.1.1.5 of [RFC7231]. 218 ETag, see section 2.3 of [RFC7232]. 220 All metadata retrieval responses SHOULD include the following 221 headers: 223 Cache-Control, see section 5.2 of [RFC7234]. 225 Content-Length, see section 3.3.2 of [RFC7230] 227 Last-Modified, see section 2.2 of [RFC7232]. 229 2.6. Status Codes 231 This protocol uses the following HTTP status codes: 233 200 "OK" - standard response code when returning requested 234 metadata 236 304 "Not Modified" - response code indicating requested metadata 237 has not been updated since the last request 239 400 "Bad Request" - response code indicating that the requester's 240 request was malformed in some fashion 242 401 "Unauthorized" - response code indicating the request must be 243 authenticated before requesting metadata 245 404 "Not Found" - indicates that the requested metadata could not 246 be found; this MUST NOT be used in order to indicate a general 247 service error. 249 405 "Method Not Allowed" - response code indicating that a non-GET 250 method was used 252 406 "Not Acceptable" - response code indicating that metadata is 253 not available in the request content-type 255 505 "HTTP Version Not Supported" - response code indicating that 256 HTTP/1.1 was not used 258 2.7. Base URL 260 Requests defined in this document are performed by issuing an HTTP 261 GET request to a particular URL ([STD66]). The final component of 262 the path to which requests are issued is defined by the requests 263 specified within this document. A base URL precedes such paths. 264 Such a base URL: 266 o MUST contain the scheme and authority components. 268 o MUST contain a path component ending with a slash ('/') character. 270 o MUST NOT include a query component. 272 o MUST NOT include a fragment identifier component. 274 2.8. Content Negotiation 276 As there may be many representations for a given piece of metadata, 277 agent-driven content negotiation is used to ensure the proper 278 representation is delivered to the requester. In addition to the 279 required usage of the Accept header a responder SHOULD also support 280 the use of the Accept-Charset header. 282 3. Metadata Query Protocol 284 The metadata query protocol retrieves metadata either for all 285 entities known to the responder or for a named collection based on a 286 single "tag" or "keyword" identifier. A request returns information 287 for none, one, or a collection of entities. 289 3.1. Identifiers 291 The query protocol uses identifiers to "tag" metadata for single- and 292 multi-entity metadata collections. The assignment of such 293 identifiers to a particular metadata document is the responsibility 294 of the query responder. If a metadata collection already contains a 295 well known identifier it is RECOMMENDED that such a natural 296 identifier is used when possible. Any given metadata collection MAY 297 have more than one identifier associated with it. 299 An identifier used in the query protocol is a non-empty sequence of 300 arbitrary 8-bit characters: 302 id = 1*idchar 303 idchar = %x00-ff ; any encodable character 305 3.2. Protocol 307 3.2.1. Request by Identifier 309 A metadata query request for all entities tagged with a particular 310 identifier is performed by issuing an HTTP GET request to a URL 311 constructed as the concatenation of the following components: 313 o The responder's base URL. 315 o The string "entities/". 317 o A single identifier, percent-encoded appropriately for use as a 318 URL path segment (see sections 2.1 and 3.3 of [STD66]). 320 For example, with a base URL of "http://example.org/mdq/", a query 321 for the identifier "foo" would be performed by an HTTP GET request to 322 the following URL: 324 http://example.org/mdq/entities/foo 326 Correct encoding of the identifier as a URL path segment is critical 327 for interoperability. In particular: 329 The character '/' MUST be percent-encoded. 331 The space character MUST be encoded as '%20' and MUST NOT be 332 encoded as '+' as would be required in a query parameter. 334 For example, with a base URL of "http://example.org/mdq/", a query 335 for the identifier ""blue/green+light blue"" would be performed by an 336 HTTP GET request to the following URL: 338 http://example.org/mdq/entities/blue%2Fgreen+light%20blue 340 3.2.2. Request All Entities 342 A metadata query request for all entities known to the responder is 343 performed by issuing an HTTP GET request to a URL constructed as the 344 concatenation of the following components: 346 o The responder's base URL. 348 o The string "entities". 350 For example, with a base URL of "http://example.org/mdq/", a query 351 for all entities would be performed by an HTTP GET request to the 352 following URL: 354 http://example.org/mdq/entities 356 3.2.3. Response 358 The response to a metadata query request MUST be a document that 359 provides metadata for the given request in the format described by 360 the request's Accept header. 362 The responder is responsible for ensuring that the metadata returned 363 is valid. If the responder can not create a valid document it MUST 364 respond with a 406 status code. An example of such an error would be 365 the case where the result of the query is metadata for multiple 366 entities but the request content type does not support returning 367 multiple results in a single document. 369 3.2.4. Example Request and Response 371 The following example demonstrates a metadata query request using a 372 base URL of "http://metadata.example.org/service/" and the identifier 373 "http://example.org/idp". 375 GET /service/entities/http:%2F%2Fexample.org%2Fidp HTTP/1.1 376 Host: metadata.example.org 377 Accept: application/samlmetadata+xml 379 Example Metadata Query Request 381 HTTP/1.x 200 OK 382 Content-Type: application/samlmetadata+xml 383 ETag: "abcdefg" 384 Last-Modified: Thu, 15 Apr 2010 12:45:26 GMT 385 Content-Length: 1234 387 388 390 .... 392 Example Metadata Query Response 394 4. Efficient Retrieval and Caching 396 4.1. Conditional Retrieval 398 Upon a successful response the responder MUST return an ETag header 399 and MAY return a Last-Modified header as well. Requesters SHOULD use 400 either or both, with the ETag being preferred, in any subsequent 401 requests for the same resource. 403 In the event that a resource has not changed since the previous 404 request, the responder SHOULD send a 304 (Not Modified) status code 405 as a response. 407 4.2. Content Caching 409 Responders SHOULD include cache control information with successful 410 (200 status code) responses, assuming the responder knows when 411 retrieved metadata is meant to expire. The responder SHOULD also 412 include cache control information with 404 Not Found responses. This 413 allows the requester to create and maintain a negative-response 414 cache. When cache controls are used only the 'max-age' directive 415 SHOULD be used. 417 4.3. Content Compression 419 As should be apparent from the required request and response headers 420 this protocol encourages the use of content compression. This is in 421 recognition that some metadata documents can be quite large or 422 fetched with relatively high frequency. 424 Requesters SHOULD support, and advertise support for, gzip 425 compression unless such usage would put exceptional demands on 426 constrained environments. Responders MUST support gzip compression. 427 Requesters and responders MAY support other compression algorithms. 429 5. Protocol Extension Points 431 The Metadata Query Protocol is extensible using the following 432 protocol extension points: 434 o Profiles of this specification may assign semantics to specific 435 identifiers, or to identifiers structured in particular ways. 437 o Profiles of this specification may define additional paths (other 438 than "entities" and "entities/") below the base URL. 440 6. Security Considerations 442 6.1. Integrity 444 As metadata often contains information necessary for the secure 445 operation of interacting services it is RECOMMENDED that some form of 446 content integrity checking be performed. This may include the use of 447 TLS at the transport layer, digital signatures present within the 448 metadata document, or any other such mechanism. 450 6.2. Confidentiality 452 In many cases service metadata is public information and therefore 453 confidentiality is not required. In the cases where such 454 functionality is required, it is RECOMMENDED that both the requester 455 and responder support TLS. Other mechanisms, such as XML encryption, 456 MAY also be supported. 458 6.3. Authentication 460 All responders which require client authentication to view retrieved 461 information MUST support the use of HTTP basic authentication 462 ([RFC7235], [RFC7617]) over TLS. Responders SHOULD also support the 463 use of X.509 client certificate authentication. 465 7. IANA Considerations 467 This document has no actions for IANA. 469 8. Acknowledgements 471 The editor would like to acknowledge the following individuals for 472 their contributions to this document: 474 Scott Cantor (The Ohio State University) 476 Leif Johansson (SUNET) 478 Thomas Lenggenhager (SWITCH) 480 Joe St Sauver (University of Oregon) 482 Tom Scavo (Internet2) 484 Special acknowledgement is due to Chad LaJoie (Covisint) for his work 485 in editing previous versions of this specification. 487 9. References 489 9.1. Normative References 491 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 492 Requirement Levels", BCP 14, RFC 2119, 493 DOI 10.17487/RFC2119, March 1997, 494 . 496 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 497 Protocol (HTTP/1.1): Message Syntax and Routing", 498 RFC 7230, DOI 10.17487/RFC7230, June 2014, 499 . 501 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 502 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 503 DOI 10.17487/RFC7231, June 2014, 504 . 506 [RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 507 Protocol (HTTP/1.1): Conditional Requests", RFC 7232, 508 DOI 10.17487/RFC7232, June 2014, 509 . 511 [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, 512 Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", 513 RFC 7234, DOI 10.17487/RFC7234, June 2014, 514 . 516 [RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 517 Protocol (HTTP/1.1): Authentication", RFC 7235, 518 DOI 10.17487/RFC7235, June 2014, 519 . 521 [RFC7617] Reschke, J., "The 'Basic' HTTP Authentication Scheme", 522 RFC 7617, DOI 10.17487/RFC7617, September 2015, 523 . 525 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 526 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 527 May 2017, . 529 [STD66] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 530 Resource Identifier (URI): Generic Syntax", STD 66, 531 RFC 3986, DOI 10.17487/RFC3986, January 2005, 532 . 534 [STD68] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 535 Specifications: ABNF", STD 68, RFC 5234, 536 DOI 10.17487/RFC5234, January 2008, 537 . 539 9.2. Informative References 541 [md-query] 542 Young, I., Ed., "md-query Project", 543 . 545 [MDX.list] 546 Young, I., Ed., "MDX Mailing List", 547 . 549 [REFEDS] Research and Education Federations, "REFEDS Home Page", 550 . 552 [REFEDS.agreement] 553 Research and Education Federations, "REFEDS Participant's 554 Agreement", 555 . 557 [RFC4844] Daigle, L., Ed. and Internet Architecture Board, "The RFC 558 Series and RFC Editor", RFC 4844, DOI 10.17487/RFC4844, 559 July 2007, . 561 Appendix A. Change Log (to be removed by RFC Editor before publication) 563 A.1. Since draft-lajoie-md-query-01 565 Adopted as base for draft-young-md-query-00. 567 Updated author and list of contributors. 569 Changed ipr from "pre5378Trust200902" to "trust200902", submission 570 type from IETF to independent and category from experimental to 571 informational. 573 Added empty IANA considerations section. 575 Minor typographical nits but (intentionally) no substantive content 576 changes. 578 A.2. Since draft-young-md-query-00 580 Split into two documents: this one is as agnostic as possible around 581 questions such as metadata format and higher level protocol use 582 cases, a new layered document describes the detailed requirements for 583 SAML support. 585 Rewrite Section 3.2.1 to clarify construction of the request URL and 586 its relationship to the base URL. 588 Added Section 2.1 to clarify that the transport protocol underlying 589 HTTP may be either TCP or SSL/TLS. 591 Clarify position on HTTP versions (Section 2.2) which may be used to 592 underly this protocol. 594 Added Change Log modelled on draft-ietf-httpbis-http2. 596 Added a reference to [STD68]. Use ABNF to describe request syntax. 597 Replace transformed identifier concept with extended identifiers 598 (this also resulted in the removal of any discussion of specific 599 transformed identifier formats). Add grammar to distinguish basic 600 from extended identifiers. 602 Changed the required response when the result can not be validly 603 expressed in the requested format from 500 to 406. 605 Removed the '+' operator and all references to multiple identifiers 606 in queries. If more complex queries are required, these will be 607 reintroduced at a different path under the base URL. 609 Added a section describing Protocol Extension Points. 611 A.3. Since draft-young-md-query-01 613 Added REFEDS RFC stream boilerplate. 615 Tidied up some normative language. 617 A.4. Since draft-young-md-query-02 619 Introduced a normative reference to [STD66]. 621 Reworked the definition of the base URL so that a non-empty path 622 ending with '/' is required. This allows the definition of request 623 URLs to be simplified. 625 Clarified the definition of the base URL to exclude a query 626 component; corrected the terminology for the fragment identifier 627 component. 629 Added the definition for the query for all entities in Section 3.2.2. 631 Corrected an example in Section 3.2.4 to include the required double 632 quotes in the value of an ETag header. Added text to clarify the 633 base URL and identifier being used in the example. 635 Simplified the definition of identifiers, so that any non-empty 636 identifier is accepted and no semantics are defined for particular 637 structures. Extended syntaxes such as the "{sha1}" notation for 638 transformed identifiers are now left to profiles. 640 Remove incidental references to SSL. 642 Remove status code 501 ("not implemented") as it is no longer 643 referenced. 645 A.5. Since draft-young-md-query-03 647 Correct a typo in the identifier grammar. 649 A.6. Since draft-young-md-query-04 651 Updated to rely on the new definition of HTTP/1.1 in [RFC7230] et 652 seq. instead of RFC 2616. 654 Corrected Section 3.2.3 to indicate that the request contains an 655 Accept header, not a Content-Type header. 657 Added an Editorial Note to help direct readers back to the 658 discussion. 660 A.7. Since draft-young-md-query-05 662 Remove unnecessary percent-encoding of a ':' character in the example 663 in Section 3.2.4. 665 Removed use of the ambiguous term "URL-encoded" in Section 3.2.1. 666 Instead, indicate that the encoding must correspond to the rules for 667 encoding a URL path segment specifically, and call out some of the 668 more important implications arising from that. Added a new example 669 illustrating these implications. 671 Updated the description of conditional retrieval in Section 4.1 to 672 make the use of a 304 (Not Modified) status code a normative but non- 673 mandatory obligation on the responder, not simply a description of 674 what the requester will receive. 676 A.8. Since draft-young-md-query-06 678 No substantive changes. 680 A.9. Since draft-young-md-query-07 682 No substantive changes. 684 A.10. Since draft-young-md-query-08 686 Modernise normative language to include [RFC8174]. 688 Reference [RFC7617] instead of the Internet-Draft. 690 Improved references to RFCs. 692 A.11. Since draft-young-md-query-09 694 No substantive changes. 696 A.12. Since draft-young-md-query-10 698 No substantive changes. 700 A.13. Since draft-young-md-query-11 702 No substantive changes. 704 A.14. Since draft-young-md-query-12 706 No substantive changes. 708 A.15. Since draft-young-md-query-13 710 No substantive changes. 712 Author's Address 714 Ian A. Young (editor) 715 Independent 717 EMail: ian@iay.org.uk