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Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-10) exists of draft-nottingham-http-link-header-06 ** Obsolete normative reference: RFC 2616 (Obsoleted by RFC 7230, RFC 7231, RFC 7232, RFC 7233, RFC 7234, RFC 7235) ** Obsolete normative reference: RFC 2818 (Obsoleted by RFC 9110) ** Obsolete normative reference: RFC 5785 (Obsoleted by RFC 8615) Summary: 3 errors (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group E. Hammer-Lahav 3 Internet-Draft Yahoo! 4 Intended status: Informational May 11, 2010 5 Expires: November 12, 2010 7 host-meta: Web Host Metadata 8 draft-hammer-hostmeta-08 10 Abstract 12 This memo describes a method for locating host metadata for Web-based 13 protocols. 15 Status of this Memo 17 This Internet-Draft is submitted in full conformance with the 18 provisions of BCP 78 and BCP 79. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF). Note that other groups may also distribute 22 working documents as Internet-Drafts. The list of current Internet- 23 Drafts is at http://datatracker.ietf.org/drafts/current/. 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as "work in progress." 30 This Internet-Draft will expire on November 12, 2010. 32 Copyright Notice 34 Copyright (c) 2010 IETF Trust and the persons identified as the 35 document authors. All rights reserved. 37 This document is subject to BCP 78 and the IETF Trust's Legal 38 Provisions Relating to IETF Documents 39 (http://trustee.ietf.org/license-info) in effect on the date of 40 publication of this document. Please review these documents 41 carefully, as they describe your rights and restrictions with respect 42 to this document. Code Components extracted from this document must 43 include Simplified BSD License text as described in Section 4.e of 44 the Trust Legal Provisions and are provided without warranty as 45 described in the Simplified BSD License. 47 Table of Contents 49 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 50 1.1. Example . . . . . . . . . . . . . . . . . . . . . . . . . 3 51 1.2. Namespace and Version . . . . . . . . . . . . . . . . . . 4 52 1.3. Notational Conventions . . . . . . . . . . . . . . . . . . 4 53 2. Metadata Scope . . . . . . . . . . . . . . . . . . . . . . . . 5 54 3. The host-meta Document Format . . . . . . . . . . . . . . . . 5 55 3.1. The 'hm:Host' Element . . . . . . . . . . . . . . . . . . 5 56 3.2. The 'Link' Element . . . . . . . . . . . . . . . . . . . . 6 57 3.2.1. Template Syntax . . . . . . . . . . . . . . . . . . . 6 58 4. Obtaining host-meta Documents . . . . . . . . . . . . . . . . 7 59 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 60 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 61 6.1. The host-meta Well-Known URI . . . . . . . . . . . . . . . 8 62 Appendix A. host-meta XML Schema . . . . . . . . . . . . . . . . 9 63 Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . . 9 64 Appendix C. Document History . . . . . . . . . . . . . . . . . . 9 65 7. Normative References . . . . . . . . . . . . . . . . . . . . . 10 66 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11 68 1. Introduction 70 Web-based protocols often require the discovery of host policy or 71 metadata, where host is not a single resource but the entity 72 controlling the collection of resources identified by Uniform 73 Resource Identifiers (URI) with a common host as defined by 74 [RFC3986]. While these protocols have a wide range of metadata 75 needs, they often define metadata that is concise, has simple syntax 76 requirements, and can benefit from storing its metadata in a common 77 location used by other related protocols. 79 Because there is no URI or resource available to describe a host, 80 many of the methods used for associating per-resource metadata (such 81 as HTTP headers) are not available. This often leads to the 82 overloading of the root HTTP resource (e.g. 'http://example.com/') 83 with host metadata that is not specific to the root resource, and 84 often has nothing to do it. 86 This memo registers the "well-known" URI suffix "host-meta" in the 87 Well-Known URI Registry established by [RFC5785], and specifies a 88 simple, general-purpose metadata document for hosts, to be used by 89 multiple Web-based protocols. 91 [[ Please discuss this draft on the apps-discuss@ietf.org [1] mailing 92 list. ]] 94 1.1. Example 96 The following is a simple host-meta document for the 'example.com' 97 and 'www.example.com' hosts with a link providing host-wide copyright 98 information and a link template providing a URI for obtaining 99 resource-specific author information for each resource within the 100 host-meta document scope: 102 103 106 example.com 107 www.example.com 109 111 Site License Policy 112 113 115 Author Profile 116 117 119 1.2. Namespace and Version 121 The host-meta document uses the XRD 1.0 XML namespace URI 122 [W3C.REC-xml-names-19990114]: 124 http://docs.oasis-open.org/ns/xri/xrd-1.0 126 The XML namespace URI for the host-meta specific extension elements 127 defined in this specification is: 129 http://host-meta.net/ns/1.0 131 1.3. Notational Conventions 133 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 134 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 135 document are to be interpreted as described in [RFC2119]. 137 Examples in this specification uses the namespace prefix "hm:" for 138 the extension Namespace URI identified in Section 1.2. The "hm:" 139 namespace prefix is arbitrary and not is semantically significant. 140 Element names without a namespace prefix belong to the XRD 1.0 XML 141 namespace identified in Section 1.2. 143 This document uses the Augmented Backus-Naur Form (ABNF) notation of 144 [RFC5234]. Additionally, the following rules are included from 145 [RFC3986]: reserved, unreserved, and host. 147 2. Metadata Scope 149 Each host-meta document describes one or more hosts, where a host is 150 not a single resource but the entity controlling the collection of 151 resources identified by URIs with a common host as defined by 152 [RFC3986], across all ports and schemes. 154 The scope MUST be expressed explicitly within the document using the 155 "hm:Host" element as described in Section 3.1. The host-meta scope 156 does not apply to any other hostname (or sub-domain) not explicitly 157 declared. For example, 'example.net', 'example.com', and 158 'www.example.com' all have different and non-overlapping scopes. 160 3. The host-meta Document Format 162 The host-meta document uses the XRD 1.0 document format as defined by 163 [OASIS.XRD-1.0], which provides a simple and extensible XML-based 164 schema for describing resources. This memo defines additional 165 elements and processing rules needed to describe hosts. Documents 166 MAY include any XRD element not explicitly excluded. 168 The host-meta document root MUST be an "XRD" element. The document 169 SHOULD NOT include a "Subject" element, as at this time no URI is 170 available to identify hosts. The use of the "Alias" element in host- 171 meta is undefined and NOT RECOMMENDED. 173 This memo defines the "hm:Host" element for declaring document scope. 174 The subject (or "context resource" as defined by 175 [I-D.nottingham-http-link-header]) of the XRD "Property" and "Link" 176 elements consists of the hosts included in the document scope. 177 However, the subject of "Link" elements with a "template" attribute 178 is the individual resources (included in the document scope) applied 179 to the link template as described in Section 3.2. 181 3.1. The 'hm:Host' Element 183 The 'hm:Host" element is used to declare the scope of the host-meta 184 document and is defined as a child element of the root "XRD" element. 185 The parent "XRD" element MUST include one but MAY include more 186 "hm:Host" elements (order does not matter). If a host-meta document 187 includes more than one "hm:Host" element, it does not signify any 188 relationship between the individual hosts other than sharing the same 189 metadata included in the document. 191 The element value syntax ABNF: 193 Host-Element-Value = host 195 3.2. The 'Link' Element 197 The XRD "Link" element, when used with the "href" attribute, conveys 198 a link relation between the hosts described by the document and a 199 common target URI. 201 For example, the following link declares a common author for the 202 entire scope: 204 206 However, a "Link" element with a "template" attribute conveys 207 relations whose context are the individual resources within the host- 208 meta document scope, and whose target is constructed by applying each 209 context resource URI to the template. The template string MAY 210 contain a URI string without any variables to represent a resource- 211 level relation that is identical for every individual resource. 213 For example, a blog with multiple authors can provide information 214 about each article's author by providing an endpoint with a parameter 215 set to the URI of each article. Each article has a unique author, 216 but all share the same pattern of where that information is located: 218 220 3.2.1. Template Syntax 222 This memo defines a simple template syntax for URI transformation. A 223 template is a string containing brace-enclosed ("{}") variable names 224 marking the parts of the string that are to be substituted by the 225 corresponding variable values. 227 Before substituting template variables, any value character other 228 than unreserved (as defined by [RFC3986]) MUST be percent-encoded per 229 [RFC3986]. 231 This memo defines a single variable - "uri" - as the entire context 232 resource URI. Protocols MAY define additional relation-specific 233 variables and syntax rules, but SHOULD only do so for protocol- 234 specific relation types, and MUST NOT change the meaning of the "uri" 235 variable. If a client is unable to successfully process a template 236 (e.g. unknown variable names, unknown or incompatible syntax) the 237 parent "Link" element SHOULD be ignored. 239 The template syntax ABNF: 241 URI-Template = *( uri-char | variable ) 242 variable = "{" var-name "}" 243 uri-char = ( reserved | unreserved ) 244 var-name = "uri" | ( 1*var-char ) 245 var-char = ALPHA / DIGIT / "." / "_" 247 For example: 249 Input: http://example.com/r?f=1 250 Template: http://example.org?q={uri} 251 Output: http://example.org?q=http%3A%2F%2Fexample.com%2Fr%3Ff%3D1 253 4. Obtaining host-meta Documents 255 Clients obtain the host-meta document for a given host by making an 256 HTTPS [RFC2818] GET request to the host's port 443 for the 257 "/.well-known/host-meta" path. If the request fails to produce a 258 valid host-meta document, clients make an HTTP [RFC2616] GET request 259 to the host's port 80 for the "/.well-known/host-meta" path. 261 Servers MUST support at least one but SHOULD support both ports. If 262 both ports are supported, they MUST serve the same document. Clients 263 MAY attempt to obtain the host-meta document from either port, SHOULD 264 attempt using port 443 first, and SHOULD attempt the other port if 265 the first fails. 267 For example, the following request is used to obtain the host-meta 268 document for the 'example.com' host: 270 GET /.well-known/host-meta HTTP/1.1 271 Host: example.com 273 If a representation is successfully obtained, but is not in the 274 format described above, clients should infer that the path is being 275 used for other purposes, and not process the response as a host-meta 276 document. To aid in this process, authorities using this mechanism 277 SHOULD correctly label host-meta responses with the 278 "application/xrd+xml" internet media type. 280 If the server response indicates that the host-meta resource is 281 located elsewhere (a 301, 302, or 307 response status code), the 282 client SHOULD try to obtain the resource from the location provided 283 in the response. This means that the host-meta document for one host 284 MAY be retrieved from a another host. Likewise, if the resource is 285 not available or does not exist (indicated respectively, by the 404 286 and 410 response status codes) at both ports, the client should infer 287 that metadata is not available via this mechanism. 289 The scope declared within the host-meta document MUST match the 290 desired host. Clients MUST NOT use host-meta documents when the 291 desired host (used to obtain the document) is not listed in the 292 document. 294 5. Security Considerations 296 The metadata returned by the host-meta resource is presumed to be 297 under the control of the appropriate authority and representative of 298 all the resources described by it. If this resource is compromised 299 or otherwise under the control of another party, it may represent a 300 risk to the security of the server and data served by it, depending 301 on what protocols use it. 303 The host-meta scope is explicitly declared by the "hm:Host" elements 304 listed in the document. Clients SHOULD evaluate the authority of a 305 host-meta document obtained from one host to describe another host. 306 Protocols that change the scope from the one declared in the document 307 without careful consideration can incur security risks. 309 Protocols using host-meta templates SHOULD evaluate the construction 310 of their templates as well as any protocol-specific variables or 311 syntax to ensure that the templates cannot be abused by an attacker. 312 For example, a client can be tricked into following a malicious link 313 due to a poorly constructed template which produces unexpected 314 results when its variable values contain unexpected characters. 316 Protocols MAY restrict document retrieval to HTTPS based on their 317 security needs. Protocols utilizing host-meta documents obtained via 318 other methods not described in this memo SHOULD consider the security 319 and authority risks associated with such methods. 321 6. IANA Considerations 323 6.1. The host-meta Well-Known URI 325 This memo registers the 'host-meta' well-known URI in the Well-Known 326 URI Registry as defined by [RFC5785]. 327 URI suffix: host-meta 328 Change controller: IETF 329 Specification document(s): [[ this document ]] 330 Related information: None 332 Appendix A. host-meta XML Schema 334 The following is the XML schema for the host-meta XRD extension 335 elements: 337 338 346 348 349 350 351 352 353 354 356 358 Appendix B. Acknowledgments 360 The author would like to acknowledge the contributions of everyone 361 who provided feedback and use cases for this memo; in particular, 362 Dirk Balfanz, DeWitt Clinton, Blaine Cook, Eve Maler, Breno de 363 Medeiros, Brad Fitzpatrick, James Manger, Will Norris, Mark 364 Nottingham, John Panzer, Drummond Reed, and Peter Saint-Andre. 366 Appendix C. Document History 368 [[ to be removed by the RFC editor before publication as an RFC ]] 370 -08 371 o Fixed typo. 373 -07 374 o Minor editorial clarifications. 375 o Added XML schema for host-meta extension. 376 o Updated XRD reference to the latest draft (no normative changes). 378 -06 379 o Updated well-known reference to RFC 5785. 380 o Minor editorial changes. 381 o Made HTTPS a higher priority (SHOULD) over HTTP. 383 -05 384 o Adjusted syntax to the latest XRD schema. 385 o Added note about using a link template without variables. 387 -04 388 o Corrected the example. 390 -03 391 o Changed scope to an entire host (per RFC 3986). 392 o Simplified template syntax to always percent-encode values and 393 vocabulary to a single 'uri' variable. 394 o Changed document retrieval to always use HTTP(S). 395 o Added security consideration about the use of templates. 396 o Explicitly defined the root element to be 'XRD'. 398 -02 399 o Changed Scope element syntax from attributes to URI-like string 400 value. 402 -01 403 o Editorial rewrite. 404 o Redefined scope as a scheme-authority pair. 405 o Added document structure section. 407 -00 408 o Initial draft. 410 7. Normative References 412 [I-D.nottingham-http-link-header] 413 Nottingham, M., "Web Linking", 414 draft-nottingham-http-link-header-06 (work in progress), 415 July 2009. 417 [OASIS.XRD-1.0] 418 Hammer-Lahav, E. and W. Norris, "Extensible Resource 419 Descriptor (XRD) Version 1.0 (work in progress)", . 423 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 424 Requirement Levels", BCP 14, RFC 2119, March 1997. 426 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., 427 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext 428 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. 430 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. 432 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 433 Resource Identifier (URI): Generic Syntax", STD 66, 434 RFC 3986, January 2005. 436 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 437 Specifications: ABNF", STD 68, RFC 5234, January 2008. 439 [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known 440 Uniform Resource Identifiers (URIs)", RFC 5785, 441 April 2010. 443 [W3C.REC-P3P-20020416] 444 Marchiori, M., "The Platform for Privacy Preferences 1.0 445 (P3P1.0) Specification", World Wide Web Consortium 446 Recommendation REC-P3P-20020416, April 2002, 447 . 449 [W3C.REC-xml-names-19990114] 450 Hollander, D., Layman, A., and T. Bray, "Namespaces in 451 XML", World Wide Web Consortium FirstEdition REC-xml- 452 names-19990114, January 1999, 453 . 455 [1] 457 Author's Address 459 Eran Hammer-Lahav 460 Yahoo! 462 Email: eran@hueniverse.com 463 URI: http://hueniverse.com