Defining Well-Known Uniform Resource Identifiers (URIs)
RFC 5785

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Internet Engineering Task Force (IETF)                     M. Nottingham
Request for Comments: 5785                               E. Hammer-Lahav
Updates: 2616, 2818                                           April 2010
Category: Standards Track
ISSN: 2070-1721

        Defining 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 in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://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 to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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 2010

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
     1.1.  Appropriate Use of Well-Known URIs  . . . . . . . . . . . . 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  . . . . . . . . . . . . . . . . . . 5
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 7
   Appendix B.  Frequently Asked Questions . . . . . . . . . . . . . . 7

1.  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 2010

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
   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