idnits 2.17.1 draft-young-md-query-09.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 (July 15, 2018) is 2112 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 July 15, 2018 5 Expires: January 16, 2019 7 Metadata Query Protocol 8 draft-young-md-query-09 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.10. 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 January 16, 2019. 47 Copyright Notice 49 Copyright (c) 2018 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 . . . . . . . . . . . . . . . . 3 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 . . . . . . . . . . . . . . . . . . . . . . . 4 68 2.4. Request Headers . . . . . . . . . . . . . . . . . . . . . 4 69 2.5. Response Headers . . . . . . . . . . . . . . . . . . . . 5 70 2.6. Status Codes . . . . . . . . . . . . . . . . . . . . . . 5 71 2.7. Base URL . . . . . . . . . . . . . . . . . . . . . . . . 6 72 2.8. Content Negotiation . . . . . . . . . . . . . . . . . . . 6 73 3. Metadata Query Protocol . . . . . . . . . . . . . . . . . . . 6 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 . . . . . . . . . . . . 8 80 4. Efficient Retrieval and Caching . . . . . . . . . . . . . . . 9 81 4.1. Conditional Retrieval . . . . . . . . . . . . . . . . . . 9 82 4.2. Content Caching . . . . . . . . . . . . . . . . . . . . . 9 83 4.3. Content Compression . . . . . . . . . . . . . . . . . . . 9 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 . . . . . . . . . . . . . . . . . . . . . 10 90 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 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) . . . . . . . . . . . . . . . . . . . . 13 96 A.1. Since draft-lajoie-md-query-01 . . . . . . . . . . . . . 13 97 A.2. Since draft-young-md-query-00 . . . . . . . . . . . . . . 13 98 A.3. Since draft-young-md-query-01 . . . . . . . . . . . . . . 14 99 A.4. Since draft-young-md-query-02 . . . . . . . . . . . . . . 14 100 A.5. Since draft-young-md-query-03 . . . . . . . . . . . . . . 14 101 A.6. Since draft-young-md-query-04 . . . . . . . . . . . . . . 14 102 A.7. Since draft-young-md-query-05 . . . . . . . . . . . . . . 15 103 A.8. Since draft-young-md-query-06 . . . . . . . . . . . . . . 15 104 A.9. Since draft-young-md-query-07 . . . . . . . . . . . . . . 15 105 A.10. Since draft-young-md-query-08 . . . . . . . . . . . . . . 15 106 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15 108 1. Introduction 110 Many clients of web-based services are capable of consuming 111 descriptive metadata about a service in order to customize or obtain 112 information about the client's connection parameters. While the form 113 of the metadata (e.g., JSON, XML) and content varies between services 114 this document specifies a set of semantics for HTTP ([RFC7230] et 115 seq.) that allow clients to rely on certain behavior. The defined 116 behavior is meant to make it easy for clients to perform queries, to 117 be efficient for both requesters and responders, and to allow the 118 responder to scale in various ways. 120 The Research and Education Federations group ([REFEDS]) is the voice 121 that articulates the mutual needs of research and education identity 122 federations worldwide. It aims to represent the requirements of 123 research and education in the ever-growing space of access and 124 identity management. 126 From time to time REFEDS will wish to publish a document in the 127 Internet RFC series. Such documents will be published as part of the 128 RFC Independent Submission Stream [RFC4844]; however the REFEDS 129 working group sign-off process will have been followed for these 130 documents, as described in the REFEDS Participant's Agreement 131 [REFEDS.agreement]. 133 This document is a product of the REFEDS Working Group process. 135 1.1. Notation and Conventions 137 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 138 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 139 "OPTIONAL" in this document are to be interpreted as described in 140 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 141 capitals, as shown here. 143 This document makes use of the Augmented BNF metalanguage defined in 144 [STD68]. 146 1.2. Terminology 148 entity: A single logical construct for which metadata may be 149 asserted. Generally this is a network accessible service. 151 metadata: A machine readable description of certain entity 152 characteristics. Generally metadata provides information such as 153 end point references, service contact information, etc. 155 2. Protocol Transport 157 The metadata query protocol seeks to fully employ the features of the 158 HTTP protocol. Additionally this specification makes mandatory some 159 optional HTTP features. 161 2.1. Transport Protocol 163 The metadata query protocol makes use of the HTTP protocol 164 ([RFC7230]) to transmit requests and responses. The underlying HTTP 165 connection MAY make use of any appropriate transport protocol. In 166 particular, the HTTP connection MAY make use of either TCP or TLS at 167 the transport layer. See the Security Considerations section for 168 guidance in choosing an appropriate transport protocol. 170 2.2. HTTP Version 172 Requests from clients MUST NOT use an HTTP version prior to version 173 1.1. Responders MUST reply to such requests using status code 505, 174 "HTTP Version Not Supported". 176 Protocol responders MUST support requests using HTTP version 1.1, and 177 MAY support later versions. 179 2.3. HTTP Method 181 All metadata query requests MUST use the GET method. 183 2.4. Request Headers 185 All metadata query requests MUST include the following HTTP headers: 187 Accept - this header MUST contain the content-type identifying the 188 type, or form, of metadata to be retrieved. See section 5.3.2 of 189 [RFC7231]. 191 All metadata query requests SHOULD include the following HTTP 192 headers: 194 Accept-Charset, see section 5.3.3 of [RFC7231] 196 Accept-Encoding, see section 5.3.4 of [RFC7231] 198 A metadata request to the same URL, after an initial request, MUST 199 include the following header: 201 If-None-Match, see section 3.2 of [RFC7232]. 203 2.5. Response Headers 205 All successful metadata query responses (even those that return no 206 results) MUST include the following headers: 208 Content-Encoding - required if, and only if, content is 209 compressed. See section 3.1.2.2 of [RFC7231]. 211 Content-Type, see section 3.1.1.5 of [RFC7231]. 213 ETag, see section 2.3 of [RFC7232]. 215 All metadata retrieval responses SHOULD include the following 216 headers: 218 Cache-Control, see section 5.2 of [RFC7234]. 220 Content-Length, see section 3.3.2 of [RFC7230] 222 Last-Modified, see section 2.2 of [RFC7232]. 224 2.6. Status Codes 226 This protocol uses the following HTTP status codes: 228 200 "OK" - standard response code when returning requested 229 metadata 231 304 "Not Modified" - response code indicating requested metadata 232 has not been updated since the last request 234 400 "Bad Request" - response code indicating that the requester's 235 request was malformed in some fashion 237 401 "Unauthorized" - response code indicating the request must be 238 authenticated before requesting metadata 239 404 "Not Found" - indicates that the requested metadata could not 240 be found; this MUST NOT be used in order to indicate a general 241 service error. 243 405 "Method Not Allowed" - response code indicating that a non-GET 244 method was used 246 406 "Not Acceptable" - response code indicating that metadata is 247 not available in the request content-type 249 505 "HTTP Version Not Supported" - response code indicating that 250 HTTP/1.1 was not used 252 2.7. Base URL 254 Requests defined in this document are performed by issuing an HTTP 255 GET request to a particular URL ([STD66]). The final component of 256 the path to which requests are issued is defined by the requests 257 specified within this document. A base URL precedes such paths. 258 Such a base URL: 260 o MUST contain the scheme and authority components. 262 o MUST contain a path component ending with a slash ('/') character. 264 o MUST NOT include a query component. 266 o MUST NOT include a fragment identifier component. 268 2.8. Content Negotiation 270 As there may be many representations for a given piece of metadata, 271 agent-driven content negotiation is used to ensure the proper 272 representation is delivered to the requester. In addition to the 273 required usage of the Accept header a responder SHOULD also support 274 the use of the Accept-Charset header. 276 3. Metadata Query Protocol 278 The metadata query protocol retrieves metadata either for all 279 entities known to the responder or for a named collection based on a 280 single "tag" or "keyword" identifier. A request returns information 281 for none, one, or a collection of entities. 283 3.1. Identifiers 285 The query protocol uses identifiers to "tag" metadata for single- and 286 multi-entity metadata collections. The assignment of such 287 identifiers to a particular metadata document is the responsibility 288 of the query responder. If a metadata collection already contains a 289 well known identifier it is RECOMMENDED that such a natural 290 identifier is used when possible. Any given metadata collection MAY 291 have more than one identifier associated with it. 293 An identifier used in the query protocol is a non-empty sequence of 294 arbitrary 8-bit characters: 296 id = 1*idchar 297 idchar = %x00-ff ; any encodable character 299 3.2. Protocol 301 3.2.1. Request by Identifier 303 A metadata query request for all entities tagged with a particular 304 identifier is performed by issuing an HTTP GET request to a URL 305 constructed as the concatenation of the following components: 307 o The responder's base URL. 309 o The string "entities/". 311 o A single identifier, percent-encoded appropriately for use as a 312 URL path segment (see sections 2.1 and 3.3 of [STD66]). 314 For example, with a base URL of "http://example.org/mdq/", a query 315 for the identifier "foo" would be performed by an HTTP GET request to 316 the following URL: 318 http://example.org/mdq/entities/foo 320 Correct encoding of the identifier as a URL path segment is critical 321 for interoperability. In particular: 323 The character '/' MUST be percent-encoded. 325 The space character MUST be encoded as '%20' and MUST NOT be 326 encoded as '+' as would be required in a query parameter. 328 For example, with a base URL of "http://example.org/mdq/", a query 329 for the identifier ""blue/green+light blue"" would be performed by an 330 HTTP GET request to the following URL: 332 http://example.org/mdq/entities/blue%2Fgreen+light%20blue 334 3.2.2. Request All Entities 336 A metadata query request for all entities known to the responder is 337 performed by issuing an HTTP GET request to a URL constructed as the 338 concatenation of the following components: 340 o The responder's base URL. 342 o The string "entities". 344 For example, with a base URL of "http://example.org/mdq/", a query 345 for all entities would be performed by an HTTP GET request to the 346 following URL: 348 http://example.org/mdq/entities 350 3.2.3. Response 352 The response to a metadata query request MUST be a document that 353 provides metadata for the given request in the format described by 354 the request's Accept header. 356 The responder is responsible for ensuring that the metadata returned 357 is valid. If the responder can not create a valid document it MUST 358 respond with a 406 status code. An example of such an error would be 359 the case where the result of the query is metadata for multiple 360 entities but the request content type does not support returning 361 multiple results in a single document. 363 3.2.4. Example Request and Response 365 The following example demonstrates a metadata query request using a 366 base URL of "http://metadata.example.org/service/" and the identifier 367 "http://example.org/idp". 369 GET /service/entities/http:%2F%2Fexample.org%2Fidp HTTP/1.1 370 Host: metadata.example.org 371 Accept: application/samlmetadata+xml 373 Example Metadata Query Request 375 HTTP/1.x 200 OK 376 Content-Type: application/samlmetadata+xml 377 ETag: "abcdefg" 378 Last-Modified: Thu, 15 Apr 2010 12:45:26 GMT 379 Content-Length: 1234 381 382 384 .... 386 Example Metadata Query Response 388 4. Efficient Retrieval and Caching 390 4.1. Conditional Retrieval 392 Upon a successful response the responder MUST return an ETag header 393 and MAY return a Last-Modified header as well. Requesters SHOULD use 394 either or both, with the ETag being preferred, in any subsequent 395 requests for the same resource. 397 In the event that a resource has not changed since the previous 398 request, the responder SHOULD send a 304 (Not Modified) status code 399 as a response. 401 4.2. Content Caching 403 Responders SHOULD include cache control information with successful 404 (200 status code) responses, assuming the responder knows when 405 retrieved metadata is meant to expire. The responder SHOULD also 406 include cache control information with 404 Not Found responses. This 407 allows the requester to create and maintain a negative-response 408 cache. When cache controls are used only the 'max-age' directive 409 SHOULD be used. 411 4.3. Content Compression 413 As should be apparent from the required request and response headers 414 this protocol encourages the use of content compression. This is in 415 recognition that some metadata documents can be quite large or 416 fetched with relatively high frequency. 418 Requesters SHOULD support, and advertise support for, gzip 419 compression unless such usage would put exceptional demands on 420 constrained environments. Responders MUST support gzip compression. 421 Requesters and responders MAY support other compression algorithms. 423 5. Protocol Extension Points 425 The Metadata Query Protocol is extensible using the following 426 protocol extension points: 428 o Profiles of this specification may assign semantics to specific 429 identifiers, or to identifiers structured in particular ways. 431 o Profiles of this specification may define additional paths (other 432 than "entities" and "entities/") below the base URL. 434 6. Security Considerations 436 6.1. Integrity 438 As metadata often contains information necessary for the secure 439 operation of interacting services it is RECOMMENDED that some form of 440 content integrity checking be performed. This may include the use of 441 TLS at the transport layer, digital signatures present within the 442 metadata document, or any other such mechanism. 444 6.2. Confidentiality 446 In many cases service metadata is public information and therefore 447 confidentiality is not required. In the cases where such 448 functionality is required, it is RECOMMENDED that both the requester 449 and responder support TLS. Other mechanisms, such as XML encryption, 450 MAY also be supported. 452 6.3. Authentication 454 All responders which require client authentication to view retrieved 455 information MUST support the use of HTTP basic authentication 456 ([RFC7235], [RFC7617]) over TLS. Responders SHOULD also support the 457 use of X.509 client certificate authentication. 459 7. IANA Considerations 461 This document has no actions for IANA. 463 8. Acknowledgements 465 The editor would like to acknowledge the following individuals for 466 their contributions to this document: 468 Scott Cantor (The Ohio State University) 470 Leif Johansson (SUNET) 471 Thomas Lenggenhager (SWITCH) 473 Joe St Sauver (University of Oregon) 475 Tom Scavo (Internet2) 477 Special acknowledgement is due to Chad LaJoie (Covisint) for his work 478 in editing previous versions of this specification. 480 9. References 482 9.1. Normative References 484 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 485 Requirement Levels", BCP 14, RFC 2119, 486 DOI 10.17487/RFC2119, March 1997, 487 . 489 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 490 Protocol (HTTP/1.1): Message Syntax and Routing", 491 RFC 7230, DOI 10.17487/RFC7230, June 2014, 492 . 494 [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 495 Protocol (HTTP/1.1): Semantics and Content", RFC 7231, 496 DOI 10.17487/RFC7231, June 2014, 497 . 499 [RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 500 Protocol (HTTP/1.1): Conditional Requests", RFC 7232, 501 DOI 10.17487/RFC7232, June 2014, 502 . 504 [RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, 505 Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching", 506 RFC 7234, DOI 10.17487/RFC7234, June 2014, 507 . 509 [RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 510 Protocol (HTTP/1.1): Authentication", RFC 7235, 511 DOI 10.17487/RFC7235, June 2014, 512 . 514 [RFC7617] Reschke, J., "The 'Basic' HTTP Authentication Scheme", 515 RFC 7617, DOI 10.17487/RFC7617, September 2015, 516 . 518 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 519 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 520 May 2017, . 522 [STD66] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 523 Resource Identifier (URI): Generic Syntax", STD 66, 524 RFC 3986, DOI 10.17487/RFC3986, January 2005, 525 . 527 [STD68] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 528 Specifications: ABNF", STD 68, RFC 5234, 529 DOI 10.17487/RFC5234, January 2008, 530 . 532 9.2. Informative References 534 [md-query] 535 Young, I., Ed., "md-query Project", 536 . 538 [MDX.list] 539 Young, I., Ed., "MDX Mailing List", 540 . 542 [REFEDS] Research and Education Federations, "REFEDS Home Page", 543 . 545 [REFEDS.agreement] 546 Research and Education Federations, "REFEDS Participant's 547 Agreement", 548 . 550 [RFC4844] Daigle, L., Ed. and Internet Architecture Board, "The RFC 551 Series and RFC Editor", RFC 4844, DOI 10.17487/RFC4844, 552 July 2007, . 554 Appendix A. Change Log (to be removed by RFC Editor before publication) 556 A.1. Since draft-lajoie-md-query-01 558 Adopted as base for draft-young-md-query-00. 560 Updated author and list of contributors. 562 Changed ipr from "pre5378Trust200902" to "trust200902", submission 563 type from IETF to independent and category from experimental to 564 informational. 566 Added empty IANA considerations section. 568 Minor typographical nits but (intentionally) no substantive content 569 changes. 571 A.2. Since draft-young-md-query-00 573 Split into two documents: this one is as agnostic as possible around 574 questions such as metadata format and higher level protocol use 575 cases, a new layered document describes the detailed requirements for 576 SAML support. 578 Rewrite Section 3.2.1 to clarify construction of the request URL and 579 its relationship to the base URL. 581 Added Section 2.1 to clarify that the transport protocol underlying 582 HTTP may be either TCP or SSL/TLS. 584 Clarify position on HTTP versions (Section 2.2) which may be used to 585 underly this protocol. 587 Added Change Log modelled on draft-ietf-httpbis-http2. 589 Added a reference to [STD68]. Use ABNF to describe request syntax. 590 Replace transformed identifier concept with extended identifiers 591 (this also resulted in the removal of any discussion of specific 592 transformed identifier formats). Add grammar to distinguish basic 593 from extended identifiers. 595 Changed the required response when the result can not be validly 596 expressed in the requested format from 500 to 406. 598 Removed the '+' operator and all references to multiple identifiers 599 in queries. If more complex queries are required, these will be 600 reintroduced at a different path under the base URL. 602 Added a section describing Protocol Extension Points. 604 A.3. Since draft-young-md-query-01 606 Added REFEDS RFC stream boilerplate. 608 Tidied up some normative language. 610 A.4. Since draft-young-md-query-02 612 Introduced a normative reference to [STD66]. 614 Reworked the definition of the base URL so that a non-empty path 615 ending with '/' is required. This allows the definition of request 616 URLs to be simplified. 618 Clarified the definition of the base URL to exclude a query 619 component; corrected the terminology for the fragment identifier 620 component. 622 Added the definition for the query for all entities in Section 3.2.2. 624 Corrected an example in Section 3.2.4 to include the required double 625 quotes in the value of an ETag header. Added text to clarify the 626 base URL and identifier being used in the example. 628 Simplified the definition of identifiers, so that any non-empty 629 identifier is accepted and no semantics are defined for particular 630 structures. Extended syntaxes such as the "{sha1}" notation for 631 transformed identifiers are now left to profiles. 633 Remove incidental references to SSL. 635 Remove status code 501 ("not implemented") as it is no longer 636 referenced. 638 A.5. Since draft-young-md-query-03 640 Correct a typo in the identifier grammar. 642 A.6. Since draft-young-md-query-04 644 Updated to rely on the new definition of HTTP/1.1 in [RFC7230] et 645 seq. instead of RFC 2616. 647 Corrected Section 3.2.3 to indicate that the request contains an 648 Accept header, not a Content-Type header. 650 Added an Editorial Note to help direct readers back to the 651 discussion. 653 A.7. Since draft-young-md-query-05 655 Remove unnecessary percent-encoding of a ':' character in the example 656 in Section 3.2.4. 658 Removed use of the ambiguous term "URL-encoded" in Section 3.2.1. 659 Instead, indicate that the encoding must correspond to the rules for 660 encoding a URL path segment specifically, and call out some of the 661 more important implications arising from that. Added a new example 662 illustrating these implications. 664 Updated the description of conditional retrieval in Section 4.1 to 665 make the use of a 304 (Not Modified) status code a normative but non- 666 mandatory obligation on the responder, not simply a description of 667 what the requester will receive. 669 A.8. Since draft-young-md-query-06 671 No substantive changes. 673 A.9. Since draft-young-md-query-07 675 No substantive changes. 677 A.10. Since draft-young-md-query-08 679 Modernise normative language to include [RFC8174]. 681 Reference [RFC7617] instead of the Internet-Draft. 683 Improved references to RFCs. 685 Author's Address 687 Ian A. Young (editor) 688 Independent 690 EMail: ian@iay.org.uk