Movatterモバイル変換

Internet Engineering Task Force (IETF)                     M. NottinghamRequest for Comments: 5785                               E. Hammer-LahavUpdates:2616,2818                                           April 2010Category: Standards TrackISSN: 2070-1721Defining Well-Known Uniform Resource Identifiers (URIs)Abstract   This memo defines a path prefix for "well-known locations",   "/.well-known/", in selected Uniform Resource Identifier (URI)   schemes.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 5741.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc5785.Copyright Notice   Copyright (c) 2010 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Nottingham & Hammer-Lahav    Standards Track                    [Page 1]

RFC 5785                Defining Well-Known URIs              April 2010Table of Contents1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .21.1.  Appropriate Use of Well-Known URIs  . . . . . . . . . . . .32.  Notational Conventions  . . . . . . . . . . . . . . . . . . . .33.  Well-Known URIs . . . . . . . . . . . . . . . . . . . . . . . .34.  Security Considerations . . . . . . . . . . . . . . . . . . . .45.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .45.1.  The Well-Known URI Registry . . . . . . . . . . . . . . . .45.1.1.  Registration Template . . . . . . . . . . . . . . . . .56.  References  . . . . . . . . . . . . . . . . . . . . . . . . . .56.1.  Normative References  . . . . . . . . . . . . . . . . . . .56.2.  Informative References  . . . . . . . . . . . . . . . . . .5Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . .7Appendix B.  Frequently Asked Questions . . . . . . . . . . . . . .71.  Introduction   It is increasingly common for Web-based protocols to require the   discovery of policy or other information about a host ("site-wide   metadata") before making a request.  For example, the Robots   Exclusion Protocol <http://www.robotstxt.org/> specifies a way for   automated processes to obtain permission to access resources;   likewise, the Platform for Privacy Preferences [W3C.REC-P3P-20020416]   tells user-agents how to discover privacy policy beforehand.   While there are several ways to access per-resource metadata (e.g.,   HTTP headers, WebDAV's PROPFIND [RFC4918]), the perceived overhead   (either in terms of client-perceived latency and/or deployment   difficulties) associated with them often precludes their use in these   scenarios.   When this happens, it is common to designate a "well-known location"   for such data, so that it can be easily located.  However, this   approach has the drawback of risking collisions, both with other such   designated "well-known locations" and with pre-existing resources.   To address this, this memo defines a path prefix in HTTP(S) URIs for   these "well-known locations", "/.well-known/".  Future specifications   that need to define a resource for such site-wide metadata can   register their use to avoid collisions and minimise impingement upon   sites' URI space.Nottingham & Hammer-Lahav    Standards Track                    [Page 2]

RFC 5785                Defining Well-Known URIs              April 20101.1.  Appropriate Use of Well-Known URIs   There are a number of possible ways that applications could use Well-   known URIs.  However, in keeping with the Architecture of the World-   Wide Web [W3C.REC-webarch-20041215], well-known URIs are not intended   for general information retrieval or establishment of large URI   namespaces on the Web.  Rather, they are designed to facilitate   discovery of information on a site when it isn't practical to use   other mechanisms; for example, when discovering policy that needs to   be evaluated before a resource is accessed, or when using multiple   round-trips is judged detrimental to performance.   As such, the well-known URI space was created with the expectation   that it will be used to make site-wide policy information and other   metadata available directly (if sufficiently concise), or provide   references to other URIs that provide such metadata.2.  Notational Conventions   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this   document are to be interpreted as described inRFC 2119 [RFC2119].3.  Well-Known URIs   A well-known URI is a URI [RFC3986] whose path component begins with   the characters "/.well-known/", and whose scheme is "HTTP", "HTTPS",   or another scheme that has explicitly been specified to use well-   known URIs.   Applications that wish to mint new well-known URIs MUST register   them, following the procedures inSection 5.1.   For example, if an application registers the name 'example', the   corresponding well-known URI on 'http://www.example.com/' would be   'http://www.example.com/.well-known/example'.   Registered names MUST conform to the segment-nz production in   [RFC3986].   Note that this specification defines neither how to determine the   authority to use for a particular context, nor the scope of the   metadata discovered by dereferencing the well-known URI; both should   be defined by the application itself.   Typically, a registration will reference a specification that defines   the format and associated media type to be obtained by dereferencing   the well-known URI.Nottingham & Hammer-Lahav    Standards Track                    [Page 3]

RFC 5785                Defining Well-Known URIs              April 2010   It MAY also contain additional information, such as the syntax of   additional path components, query strings and/or fragment identifiers   to be appended to the well-known URI, or protocol-specific details   (e.g., HTTP [RFC2616] method handling).   Note that this specification does not define a format or media-type   for the resource located at "/.well-known/" and clients should not   expect a resource to exist at that location.4.  Security Considerations   This memo does not specify the scope of applicability of metadata or   policy obtained from a well-known URI, and does not specify how to   discover a well-known URI for a particular application.  Individual   applications using this mechanism must define both aspects.   Applications minting new well-known URIs, as well as administrators   deploying them, will need to consider several security-related   issues, including (but not limited to) exposure of sensitive data,   denial-of-service attacks (in addition to normal load issues), server   and client authentication, vulnerability to DNS rebinding attacks,   and attacks where limited access to a server grants the ability to   affect how well-known URIs are served.5.  IANA Considerations5.1.  The Well-Known URI Registry   This document establishes the well-known URI registry.   Well-known URIs are registered on the advice of one or more   Designated Experts (appointed by the IESG or their delegate), with a   Specification Required (using terminology from [RFC5226]).  However,   to allow for the allocation of values prior to publication, the   Designated Expert(s) may approve registration once they are satisfied   that such a specification will be published.   Registration requests should be sent to the   wellknown-uri-review@ietf.org mailing list for review and comment,   with an appropriate subject (e.g., "Request for well-known URI:   example").   Before a period of 14 days has passed, the Designated Expert(s) will   either approve or deny the registration request, communicating this   decision both to the review list and to IANA.  Denials should include   an explanation and, if applicable, suggestions as to how to make theNottingham & Hammer-Lahav    Standards Track                    [Page 4]

RFC 5785                Defining Well-Known URIs              April 2010   request successful.  Registration requests that are undetermined for   a period longer than 21 days can be brought to the IESG's attention   (using the iesg@iesg.org mailing list) for resolution.5.1.1.  Registration Template   URI suffix:  The name requested for the well-known URI, relative to      "/.well-known/"; e.g., "example".   Change controller:  For Standards-Track RFCs, state "IETF".  For      others, give the name of the responsible party.  Other details      (e.g., postal address, e-mail address, home page URI) may also be      included.   Specification document(s):  Reference to the document that specifies      the field, preferably including a URI that can be used to retrieve      a copy of the document.  An indication of the relevant sections      may also be included, but is not required.   Related information:  Optionally, citations to additional documents      containing further relevant information.6.  References6.1.  Normative References   [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate             Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC3986] Berners-Lee, T., Fielding, R., and L.  Masinter, "Uniform             Resource Identifier (URI): Generic Syntax", STD 66,RFC 3986, January 2005.   [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an             IANA Considerations Section in RFCs",BCP 26,RFC 5226,             May 2008.6.2.  Informative References   [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter,             L., Leach, P., and T. Berners-Lee, "Hypertext Transfer             Protocol -- HTTP/1.1",RFC 2616, June 1999.   [RFC4918] Dusseault, L., "HTTP Extensions for Web Distributed             Authoring and Versioning (WebDAV)",RFC 4918, June 2007.Nottingham & Hammer-Lahav    Standards Track                    [Page 5]

RFC 5785                Defining Well-Known URIs              April 2010   [W3C.REC-P3P-20020416]             Marchiori, M., "The Platform for Privacy Preferences 1.0             (P3P1.0) Specification", World Wide Web Consortium             Recommendation REC-P3P-20020416, April 2002,             <http://www.w3.org/TR/2002/ REC-P3P-20020416>.   [W3C.REC-webarch-20041215]             Jacobs, I. and N. Walsh, "Architecture of the World Wide             Web, Volume One", World Wide Web Consortium             Recommendation REC- webarch-20041215, December 2004,             <http:// www.w3.org/TR/2004/REC-webarch-20041215>.Nottingham & Hammer-Lahav    Standards Track                    [Page 6]

RFC 5785                Defining Well-Known URIs              April 2010Appendix A.  Acknowledgements   We would like to acknowledge the contributions of everyone who   provided feedback and use cases for this document; in particular,   Phil Archer, Dirk Balfanz, Adam Barth, Tim Bray, Brian Eaton, Brad   Fitzpatrick, Joe Gregorio, Paul Hoffman, Barry Leiba, Ashok Malhotra,   Breno de Medeiros, John Panzer, and Drummond Reed.  However, they are   not responsible for errors and omissions.Appendix B.  Frequently Asked Questions   1. Aren't well-known locations bad for the Web?      They are, but for various reasons -- both technical and social --      they are commonly used and their use is increasing.  This memo      defines a "sandbox" for them, to reduce the risks of collision and      to minimise the impact upon pre-existing URIs on sites.   2. Why /.well-known?      It's short, descriptive, and according to search indices, not      widely used.   3. What impact does this have on existing mechanisms, such as P3P and      robots.txt?      None, until they choose to use this mechanism.   4. Why aren't per-directory well-known locations defined?      Allowing every URI path segment to have a well-known location      (e.g., "/images/.well-known/") would increase the risks of      colliding with a pre-existing URI on a site, and generally these      solutions are found not to scale well, because they're too      "chatty".Nottingham & Hammer-Lahav    Standards Track                    [Page 7]

RFC 5785                Defining Well-Known URIs              April 2010Authors' Addresses   Mark Nottingham   EMail: mnot@mnot.net   URI:http://www.mnot.net/   Eran Hammer-Lahav   EMail: eran@hueniverse.com   URI:http://hueniverse.com/Nottingham & Hammer-Lahav    Standards Track                    [Page 8]