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Versions: 00 01 02 03 04 05 RFC 5785

Network Working Group                                      M. Nottingham
Internet-Draft                                           E. Hammer-Lahav
Intended status: Informational                        September 17, 2009
Expires: March 21, 2010


                        Defining Well-Known URIs
                     draft-nottingham-site-meta-03

Status of this Memo

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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
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Abstract

   This memo defines a path prefix for "well-known locations" in URIs.





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Table of Contents

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





























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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 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
   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 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.

   Please discuss this draft on the apps-discuss@ietf.org [1] mailing
   list.


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 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/".

   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 value 'example', the
   corresponding well-known URI on 'http://www.example.com/' would be
   'http://www.example.com/.well-known/example'.

   Note that this specification defines neither how to determine the



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   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 at 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.

   An attacker with certain types of limited access to a server may be
   able to affect how well-known URIs are served; for example, they may
   be able to upload a file at that location, or they may be able to
   cause a server to redirect a well-known URI to a URI that they
   control.

   Because most URI schemes rely on DNS to resolve names, they are
   vulnerable to "DNS rebinding" attacks, whereby a request can be
   directed to a server under the control of an attacker.


5.  IANA Considerations

5.1.  The Well-Known URI Registry

   This document establishes the well-known URI registry as the name
   space of URIs that have a path beginning with "/.well-known/".

   Well-known URIs are registered on the advice of a Designated Expert
   (appointed by the IESG or their delegate), with a Specification
   Required (using terminology from [RFC5226]).

   Registration requests consist of the completed registration template



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   (see Section 5.1.1), typically published in an RFC or Open Standard
   (in the sense described by [RFC2026], section 7).  However, to allow
   for the allocation of values prior to publication, the Designated
   Expert may approve registration once they are satisfied that an RFC
   (or other Open Standard) will be published.

   Upon receiving a registration request (usually via IANA), the
   Designated Expert should request review and comment from the apps-
   discuss mailing list (or a successor designated by the APPS Area
   Directors).  Before a period of 30 days has passed, the Designated
   Expert 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.

5.1.1.  Registration Template

   URI suffix:  The name requested for the well-known URI, relative to
      "/.well-known/"; e.g., "example".  MUST conform to the segment-nz
      production in [RFC3986].
   Change controller:  For standards-track RFCs, state "IETF".  For
      other open standards, give the name of the publishing body (e.g.,
      ANSI, ISO, ITU, W3C, etc.).  A postal address, home page URI,
      telephone and fax numbers may also be included.
   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

   [RFC2026]  Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996.

   [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,



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              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.

URIs

   [1]  <https://www.ietf.org/mailman/listinfo/apps-discuss>


Appendix A.  Acknowledgements

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

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.







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B.3.  Is this just for HTTP URIs?

   No; although HTTP is the most typical use case, applications can
   define well-known URIs for any URI scheme that allows path segments.

B.4.  What impact does this have on existing mechanisms, such as P3P and
      robots.txt?

   None, until they choose to use this mechanism.

B.5.  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  -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/






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   Eran Hammer-Lahav

   Email: eran@hueniverse.com
   URI:   http://hueniverse.com/















































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