Defining Well-Known Uniform Resource Identifiers (URIs)
draft-nottingham-site-meta-05

Network Working Group                                      M. Nottingham
Internet-Draft                                           E. Hammer-Lahav
Updates: 2616 2818                                     December 30, 2009
(if approved)
Intended status: Standards Track
Expires: July 3, 2010

                        Defining Well-Known URIs
                     draft-nottingham-site-meta-05

Abstract

   This memo defines a path prefix for "well-known locations", "/.well-
   known/" in selected URI schemes.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on July 3, 2010.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 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

Nottingham & Hammer-Lahav  Expires July 3, 2010                 [Page 1]
Internet-Draft          Defining Well-Known URIs           December 2009

   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 BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Appropriate Use of Well-Known URIs  . . . . . . . . . . . . 3
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . . . 3
   3.  Well-Known URIs . . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
     5.1.  The Well-Known URI Registry . . . . . . . . . . . . . . . . 5
       5.1.1.  Registration Template . . . . . . . . . . . . . . . . . 5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 6
   Appendix B.  Frequently Asked Questions . . . . . . . . . . . . . . 7
     B.1.  Aren't well-known locations bad for the Web?  . . . . . . . 7
     B.2.  Why /.well-known? . . . . . . . . . . . . . . . . . . . . . 7
     B.3.  What impact does this have on existing mechanisms,
           such as P3P and robots.txt? . . . . . . . . . . . . . . . . 7
     B.4.  Why aren't per-directory well-known locations defined?  . . 7
   Appendix C.  Document History . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8

Nottingham & Hammer-Lahav  Expires July 3, 2010                 [Page 2]
Internet-Draft          Defining Well-Known URIs           December 2009

1.  Introduction

   It is increasingly common for Web-based protocols to require the
   discovery of policy or 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 metadata, 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.

1.1.  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
   name-spaces 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",

Nottingham & Hammer-Lahav  Expires July 3, 2010                 [Page 3]
Internet-Draft          Defining Well-Known URIs           December 2009

   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 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 which has explicitly been specified to use well-
   known URIs.

   Applications that wish to mint new well-known URIs MUST register
   them, following the procedures in Section 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.

   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 also 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

Nottingham & Hammer-Lahav  Expires July 3, 2010                 [Page 4]
Internet-Draft          Defining Well-Known URIs           December 2009

   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 Considerations

5.1.  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 [TBD]@ietf.org mailing
   list for review and comment, with an appropriate subject (e.g.,
   "Request for well-known URI: example").

   [[NOTE TO RFC-EDITOR: The name of the mailing list should be
   determined in consultation with the IESG and IANA.  Suggested name:
   wellknown-uri-review. ]]

   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 the
   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.

Nottingham & Hammer-Lahav  Expires July 3, 2010                 [Page 5]
Internet-Draft          Defining Well-Known URIs           December 2009

   Specification document(s):  Reference to 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.  References

6.1.  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.

   [W3C.REC-P3P-20020416]
              Marchiori, M., "The Platform for Privacy Preferences 1.0
              (P3P1.0) Specification", W3C REC REC-P3P-20020416,
              April 2002.

   [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>.

Appendix A.  Acknowledgements

   We would like to acknowledge the contributions of everyone who
   provided feedback and use cases for this draft; in particular, Phil

Nottingham & Hammer-Lahav  Expires July 3, 2010                 [Page 6]
Internet-Draft          Defining Well-Known URIs           December 2009

   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

B.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.

B.2.  Why /.well-known?

   It's short, descriptive and according to search indices, not widely
   used.

B.3.  What impact does this have on existing mechanisms, such as P3P and
      robots.txt?

   None, until they choose to use this mechanism.

B.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".

Appendix C.  Document History

   [[RFC Editor: please remove this section before publication.]]

   o  -05
      *  Note that lack of a decision by the expert can be appealed to
         the IESG.
      *  Clarify status of specifications suitable for registration.
      *  Add reference for Robots Exclusion Protocol.
      *  Clarify appropriate use cases.
   o  -04
      *  Restrict to HTTP(S) by default.
      *  Shorten review SLA to 14 days.

Nottingham & Hammer-Lahav  Expires July 3, 2010                 [Page 7]
Internet-Draft          Defining Well-Known URIs           December 2009

      *  Allow for multiple designated experts.
      *  Identify mailing list for request submission and discussion.
   o  -03
      *  Add fragment identifiers to list of things an application might
         define.
      *  Note that the /.well-known/ URI doesn't have anything there.
   o  -02
      *  Rewrote to just define a namespace for well-known URIs.
      *  Changed discussion forum to apps-discuss.
   o  -01
      *  Changed "site-meta" to "host-meta" after feedback.
      *  Changed from XML to text-based header-like format.
      *  Remove capability for generic inline content.
      *  Added registry for host-meta fields.
      *  Clarified scope of metadata application.
      *  Added security consideration about HTTP vs. HTTPS, expanding
         scope.

Authors' 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  Expires July 3, 2010                 [Page 8]