< draft-nottingham-rfc5785bis-01.txt   draft-nottingham-rfc5785bis-02.txt >
Network Working Group M. Nottingham Network Working Group M. Nottingham
Internet-Draft November 13, 2017 Internet-Draft February 5, 2018
Obsoletes: 5785 (if approved) Obsoletes: 5785 (if approved)
Intended status: Standards Track Intended status: Standards Track
Expires: May 17, 2018 Expires: August 9, 2018
Defining Well-Known Uniform Resource Identifiers (URIs) Defining Well-Known Uniform Resource Identifiers (URIs)
draft-nottingham-rfc5785bis-01 draft-nottingham-rfc5785bis-02
Abstract Abstract
This memo defines a path prefix for "well-known locations", "/.well- This memo defines a path prefix for "well-known locations", "/.well-
known/", in selected Uniform Resource Identifier (URI) schemes. known/", in selected Uniform Resource Identifier (URI) schemes.
Note to Readers Note to Readers
_RFC EDITOR: please remove this section before publication_ _RFC EDITOR: please remove this section before publication_
This draft is a proposed revision of RFC5875. This draft is a proposed revision of RFC5875.
The issues list for this draft can be found at The issues list for this draft can be found at
https://github.com/mnot/I-D/labels/5785bis . https://github.com/mnot/I-D/labels/5785bis [1].
The most recent (often, unpublished) draft is at The most recent (often, unpublished) draft is at
https://mnot.github.io/I-D/5785bis/ . https://mnot.github.io/I-D/5785bis/ [2].
Recent changes are listed at https://github.com/mnot/I-D/commits/gh- Recent changes are listed at https://github.com/mnot/I-D/commits/gh-
pages/5785bis . pages/5785bis [3].
See also the draft's current status in the IETF datatracker, at See also the draft's current status in the IETF datatracker, at
https://datatracker.ietf.org/doc/draft-nottingham-5785bis/ . https://datatracker.ietf.org/doc/draft-nottingham-5785bis/ [4].
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 17, 2018. This Internet-Draft will expire on August 9, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Appropriate Use of Well-Known URIs . . . . . . . . . . . 3 1.1. Appropriate Use of Well-Known URIs . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . 4
3. Well-Known URIs . . . . . . . . . . . . . . . . . . . . . . . 4 3. Well-Known URIs . . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5.1. The Well-Known URI Registry . . . . . . . . . . . . . . . 5 5.1. The Well-Known URI Registry . . . . . . . . . . . . . . . 5
5.1.1. Registration Template . . . . . . . . . . . . . . . . 5 5.1.1. Registration Template . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 5 6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 6 6.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Frequently Asked Questions . . . . . . . . . . . . . 6 6.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Appendix B. Changes from RFC5785 . . . . . . . . . . . . . . . . 7 Appendix A. Frequently Asked Questions . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 Appendix B. Changes from RFC5785 . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
Some applications on the Web require the discovery of policy or other Some applications on the Web require the discovery of policy or other
information about an origin [RFC6454] (sometimes called "site-wide information about an origin [RFC6454] (sometimes called "site-wide
metadata") before making a request. For example, the Robots metadata") before making a request. For example, the Robots
Exclusion Protocol (http://www.robotstxt.org/ ) specifies a way for Exclusion Protocol (http://www.robotstxt.org/ [5]) specifies a way
automated processes to obtain permission to access resources; for automated processes to obtain permission to access resources;
likewise, the Platform for Privacy Preferences [W3C.REC-P3P-20020416] likewise, the Platform for Privacy Preferences [W3C.REC-P3P-20020416]
tells user-agents how to discover privacy policy before interacting tells user-agents how to discover privacy policy before interacting
with a site. with an origin server.
While there are several ways to access per-resource metadata (e.g., While there are several ways to access per-resource metadata (e.g.,
HTTP headers, WebDAV's PROPFIND [RFC4918]), the perceived overhead HTTP headers, WebDAV's PROPFIND [RFC4918]), the perceived overhead
(either in terms of client-perceived latency and/or deployment (either in terms of client-perceived latency and/or deployment
difficulties) associated with them often precludes their use in these difficulties) associated with them often precludes their use in these
scenarios. scenarios.
When this happens, one solution is designating a "well-known When this happens, one solution is designating a "well-known
location" for data or services related to the origin, so that it can location" for data or services related to the origin, so that it can
be easily located. However, this approach has the drawback of be easily located. However, this approach has the drawback of
risking collisions, both with other such designated "well-known risking collisions, both with other such designated "well-known
locations" and with pre-existing resources. locations" and with pre-existing resources.
To address this, this memo defines a path prefix in HTTP(S) URIs for To address this, this memo defines a path prefix in HTTP(S) URIs for
these "well-known locations", "/.well-known/". Future specifications these "well-known locations", "/.well-known/". Future specifications
that need to define a resource for such site-wide metadata can that need to define a resource for such metadata can register their
register their use to avoid collisions and minimise impingement upon use to avoid collisions and minimise impingement upon origins' URI
sites' URI space. space.
Well-known URIs can also be used with other URI schemes, but only Well-known URIs can also be used with other URI schemes, but only
when those schemes' definitions explicitly allow it. when those schemes' definitions explicitly allow it.
1.1. Appropriate Use of Well-Known URIs 1.1. Appropriate Use of Well-Known URIs
There are a number of possible ways that applications could use well- There are a number of possible ways that applications could use well-
known URIs. However, in keeping with the Architecture of the World- known URIs. However, in keeping with the Architecture of the World-
Wide Web [W3C.REC-webarch-20041215], well-known URIs are not intended Wide Web [W3C.REC-webarch-20041215], well-known URIs are not intended
for general information retrieval or establishment of large URI for general information retrieval or establishment of large URI
namespaces on the Web. Rather, they are designed to facilitate namespaces.
discovery of information on a site when it isn't practical to use
other mechanisms; for example, when discovering policy that needs to Rather, they are designed to facilitate discovery of information
be evaluated before a resource is accessed, or when using multiple about an origin when it isn't practical to use other mechanisms; for
round-trips is judged detrimental to performance. example, when discovering policy that needs to be evaluated before a
resource is accessed, or when the information applies to many (or
all) of the origin's resources.
As such, the well-known URI space was created with the expectation As such, the well-known URI space was created with the expectation
that it will be used to make policy information and other metadata that it will be used to make policy information and other metadata
about the origin available directly (if sufficiently concise), or about the origin available directly (if sufficiently concise), or
provide references to other URIs that provide it. provide references to other URIs that provide it. In general, the
information it contains should be applicable to most Web origins
(while acknowledging that many will not use a particular well-known
location, for various reasons).
Therefore, it is inappropriate to use well-known URIs as a means of In particular, well-known URIs are not a "protocol registry" for
identifying or locating a new protocol built on top of HTTP, since applications and protocols that wish to use HTTP as a substrate.
they are intended for metadata about their origin. Even if a particular origin is dedicated to the protocol in question,
it is inappropriate to devote a URL on all origins to a specialist
protocol that has little or no potential benefit for them.
In particular, locating information using a hostname instead of a URI Instead, such applications and protocols are encouraged to used a URI
is, on its own, insufficient reason to register a well-known URI. to bootstrap their operation, rather than using a hostname and a
well-known URI.
Exceptionally, the registry expert(s) may approve such a registration
for documents in the IETF Stream [RFC5741], in consultation with the
IESG, provided that the protocol in question cannot be bootstrapped
with a URI (e.g., the discovery mechanism can only carry a hostname).
However, merely making it easier to locate it is not a sufficient
reason. Likewise, future use unsupported by the specification in
question is not sufficient reason to register a well-known location.
Well-known locations are also not suited for information on topics
other than the origin that they are located upon; for example,
creating a well-known resource about a business entity or
organisational structure presumes that Internet hosts and
organisations share structure, and are likely to have significant
deployment issues in environments where this is not true.
2. Notational Conventions 2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
3. Well-Known URIs 3. Well-Known URIs
A well-known URI is a URI [RFC3986] whose path component begins with A well-known URI is a URI [RFC3986] whose path component begins with
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It MAY also contain additional information, such as the syntax of It MAY also contain additional information, such as the syntax of
additional path components, query strings and/or fragment identifiers additional path components, query strings and/or fragment identifiers
to be appended to the well-known URI, or protocol-specific details to be appended to the well-known URI, or protocol-specific details
(e.g., HTTP [RFC7231] method handling). (e.g., HTTP [RFC7231] method handling).
Note that this specification does not define a format or media-type Note that this specification does not define a format or media-type
for the resource located at "/.well-known/" and clients should not for the resource located at "/.well-known/" and clients should not
expect a resource to exist at that location. expect a resource to exist at that location.
Well-known URIs are only valid when rooted in the top of the path's
hierarchy; they MUST NOT be used in other parts of the path. For
example, "/.well-known/example" is a valid use, but "/foo/.well-
known/example" is not.
4. Security Considerations 4. Security Considerations
This memo does not specify the scope of applicability of metadata or 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 policy obtained from a well-known URI, and does not specify how to
discover a well-known URI for a particular application. Individual discover a well-known URI for a particular application. Individual
applications using this mechanism must define both aspects. applications using this mechanism must define both aspects.
Applications minting new well-known URIs, as well as administrators Applications minting new well-known URIs, as well as administrators
deploying them, will need to consider several security-related deploying them, will need to consider several security-related
issues, including (but not limited to) exposure of sensitive data, issues, including (but not limited to) exposure of sensitive data,
denial-of-service attacks (in addition to normal load issues), server denial-of-service attacks (in addition to normal load issues), server
and client authentication, vulnerability to DNS rebinding attacks, and client authentication, vulnerability to DNS rebinding attacks,
and attacks where limited access to a server grants the ability to and attacks where limited access to a server grants the ability to
affect how well-known URIs are served. affect how well-known URIs are served.
Security-sensitive applications using well-known locations should
consider that some server administrators might be unaware of its
existence (especially on operating systems that hide directories
whose names begin with "."). This means that if an attacker has
write access to the .well-known directory, they would be able to
control its contents, possibly without the administrator realising
it.
5. IANA Considerations 5. IANA Considerations
5.1. The Well-Known URI Registry 5.1. The Well-Known URI Registry
This document specifies procedures for the well-known URI registry, This document specifies procedures for the well-known URI registry,
first defined in [RFC5785]. first defined in [RFC5785].
Well-known URIs are registered on the advice of one or more experts Well-known URIs are registered on the advice of one or more experts
(appointed by the IESG or their delegate), with a Specification (appointed by the IESG or their delegate), with a Specification
Required (using terminology from [RFC8126]). However, to allow for Required (using terminology from [RFC8126]).
the allocation of values prior to publication, the expert(s) may
approve registration once they are satisfied that such a To allow for the allocation of values prior to publication, the
specification will be published. expert(s) may approve registration once they are satisfied that such
a specification will be published.
Registration requests can be sent to the wellknown-uri- Registration requests can be sent to the wellknown-uri-
review@ietf.org mailing list for review and comment, with an review@ietf.org mailing list for review and comment, with an
appropriate subject (e.g., "Request for well-known URI: example"). appropriate subject (e.g., "Request for well-known URI: example").
5.1.1. Registration Template 5.1.1. Registration Template
URI suffix: The name requested for the well-known URI, relative to URI suffix: The name requested for the well-known URI, relative to
"/.well-known/"; e.g., "example". "/.well-known/"; e.g., "example".
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may also be included, but is not required. may also be included, but is not required.
Related information: Optionally, citations to additional documents Related information: Optionally, citations to additional documents
containing further relevant information. containing further relevant information.
6. References 6. References
6.1. Normative References 6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119,
RFC2119, March 1997, <https://www.rfc-editor.org/info/ DOI 10.17487/RFC2119, March 1997,
rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC Resource Identifier (URI): Generic Syntax", STD 66,
3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454, DOI [RFC5741] Daigle, L., Ed., Kolkman, O., Ed., and IAB, "RFC Streams,
10.17487/RFC6454, December 2011, <https://www.rfc- Headers, and Boilerplates", RFC 5741,
editor.org/info/rfc6454>. DOI 10.17487/RFC5741, December 2009,
<https://www.rfc-editor.org/info/rfc5741>.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011,
<https://www.rfc-editor.org/info/rfc6454>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
6.2. Informative References 6.2. Informative References
[RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed [RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed
Authoring and Versioning (WebDAV)", RFC 4918, DOI Authoring and Versioning (WebDAV)", RFC 4918,
10.17487/RFC4918, June 2007, <https://www.rfc- DOI 10.17487/RFC4918, June 2007,
editor.org/info/rfc4918>. <https://www.rfc-editor.org/info/rfc4918>.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785, DOI Uniform Resource Identifiers (URIs)", RFC 5785,
10.17487/RFC5785, April 2010, <https://www.rfc- DOI 10.17487/RFC5785, April 2010,
editor.org/info/rfc5785>. <https://www.rfc-editor.org/info/rfc5785>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
10.17487/RFC7231, June 2014, <https://www.rfc- DOI 10.17487/RFC7231, June 2014,
editor.org/info/rfc7231>. <https://www.rfc-editor.org/info/rfc7231>.
[W3C.REC-P3P-20020416] [W3C.REC-P3P-20020416]
Marchiori, M., "The Platform for Privacy Preferences 1.0 Marchiori, M., "The Platform for Privacy Preferences 1.0
(P3P1.0) Specification", World Wide Web Consortium (P3P1.0) Specification", World Wide Web Consortium
Recommendation REC-P3P-20020416, April 2002, Recommendation REC-P3P-20020416, April 2002,
<http://www.w3.org/TR/2002/REC-P3P-20020416>. <http://www.w3.org/TR/2002/REC-P3P-20020416>.
6.3. URIs
[1] https://github.com/mnot/I-D/labels/5785bis
[2] https://mnot.github.io/I-D/5785bis/
[3] https://github.com/mnot/I-D/commits/gh-pages/5785bis
[4] https://datatracker.ietf.org/doc/draft-nottingham-5785bis/
[5] http://www.robotstxt.org/
Appendix A. Frequently Asked Questions Appendix A. Frequently Asked Questions
1. Aren't well-known locations bad for the Web? 1. Aren't well-known locations bad for the Web?
They are, but for various reasons - both technical and social - They are, but for various reasons - both technical and social -
they are sometimes necessary. This memo defines a "sandbox" for they are sometimes necessary. This memo defines a "sandbox" for
them, to reduce the risks of collision and to minimise the impact them, to reduce the risks of collision and to minimise the impact
upon pre-existing URIs on sites. upon pre-existing URIs on sites.
2. Why /.well-known? 2. Why /.well-known?
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Appendix A. Frequently Asked Questions Appendix A. Frequently Asked Questions
1. Aren't well-known locations bad for the Web? 1. Aren't well-known locations bad for the Web?
They are, but for various reasons - both technical and social - They are, but for various reasons - both technical and social -
they are sometimes necessary. This memo defines a "sandbox" for they are sometimes necessary. This memo defines a "sandbox" for
them, to reduce the risks of collision and to minimise the impact them, to reduce the risks of collision and to minimise the impact
upon pre-existing URIs on sites. upon pre-existing URIs on sites.
2. Why /.well-known? 2. Why /.well-known?
It's short, descriptive, and according to search indices, not It's short, descriptive, and according to search indices, not
widely used. widely used.
3. What impact does this have on existing mechanisms, such as P3P 3. What impact does this have on existing mechanisms, such as P3P
and robots.txt? and robots.txt?
None, until they choose to use this mechanism. None, until they choose to use this mechanism.
4. Why aren't per-directory well-known locations defined? 4. Why aren't per-directory well-known locations defined?
Allowing every URI path segment to have a well-known location Allowing every URI path segment to have a well-known location
(e.g., "/images/.well-known/") would increase the risks of (e.g., "/images/.well-known/") would increase the risks of
colliding with a pre-existing URI on a site, and generally these colliding with a pre-existing URI on a site, and generally these
solutions are found not to scale well, because they're too solutions are found not to scale well, because they're too
"chatty". "chatty".
5. I want to use a well-known location to make it easy to configure
my protocol that uses HTTP.
This is not what well-known locations are for; see Section 1.1.
Appendix B. Changes from RFC5785 Appendix B. Changes from RFC5785
o Discuss inappropriate uses more fully o Discuss appropriate and inappropriate uses more fully
o Adjusted IANA instructions o Adjust IANA instructions
o Updated references o Update references
o Various other clarifications o Various other clarifications
Author's Address Author's Address
Mark Nottingham Mark Nottingham
Email: mnot@mnot.net Email: mnot@mnot.net
URI: https://www.mnot.net/ URI: https://www.mnot.net/
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