wdiff draft-nottingham-rfc5785bis-04.txt draft-nottingham-rfc5785bis-05.txt

Network Working Group M. Nottingham
Internet-Draft February 15, April 5, 2018
Obsoletes: 5785 (if approved)
Intended status: Standards Track
Expires: August 19, October 7, 2018

Defining Well-Known Uniform Resource Identifiers (URIs)
draft-nottingham-rfc5785bis-04
draft-nottingham-rfc5785bis-05

Abstract

This memo defines a path prefix for "well-known locations", "/.well-
known/", in selected Uniform Resource Identifier (URI) schemes.

Note to Readers

_RFC EDITOR: please remove this section before publication_

This draft is a proposed revision of RFC5875.

The issues list for this draft can be found at
https://github.com/mnot/I-D/labels/rfc5785bis [1].

The most recent (often, unpublished) draft is at
https://mnot.github.io/I-D/rfc5785bis/ [2].

Recent changes are listed at https://github.com/mnot/I-D/commits/gh-
pages/rfc5785bis [3].

See also the draft's current status in the IETF datatracker, at
https://datatracker.ietf.org/doc/draft-nottingham-rfc5785bis/ [4].

Status of This Memo

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

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on August 19, October 7, 2018.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Appropriate Use of Well-Known URIs
2. Notational Conventions . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . 3
3. Well-Known URIs . . . . . . . . . . . 4
3. Well-Known URIs . . . . . . . . . . . . 3
3.1. Registering Well-Known URIs . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations
4.1. Interaction with the Web . . . . . . . . . . . . . . . . 5
4.2. Scoping Applications . . . . . 5
5.1. The Well-Known URI Registry . . . . . . . . . . . . . 6
4.3. Hidden Capabilities . . 5
5.1.1. Registration Template . . . . . . . . . . . . . . . . 6 . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5.1. The Well-Known URI Registry . . . . . . . . . . . . . . . 7
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 7
6.1. Normative References . . . . . . . . . . . . . . . . . . 6 7
6.2. Informative References . . . . . . . . . . . . . . . . . 7 8
6.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 7 9
Appendix A. Frequently Asked Questions . . . . . . . . . . . . . 8 9
Appendix B. Changes from RFC5785 . . . . . . . . . . . . . . . . 8 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 10

1. Introduction

Some applications on the Web require the discovery of information
about an origin [RFC6454] (sometimes called "site-wide metadata")
before making a request. For example, the Robots Exclusion Protocol
(http://www.robotstxt.org/ [5]) 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 before interacting with an
origin server.

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, one solution is designating a "well-known
location" for data or services related to the origin overall, 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 resources that the origin has created (or wishes
to create).

At the same time, it has become more popular to use HTTP as a
substrate for non-Web protocols. Sometimes, such protocols need a
way to locate one or more resources on a given host.

To address this, these uses, 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 metadata can
register their use to avoid collisions and minimise impingement upon
origins' URI space.

Well-known URIs can also be used with other URI schemes, but only
when those schemes' definitions explicitly allow it.

1.1. Appropriate Use of Well-Known URIs

As per [RFC7320], "publishing independent standards that mandate
particular forms of URI substructure is inappropriate, because that
essentially usurps ownership." Well-known URIs are not an escape
hatch from the requirements therein; they are a very limited carve-
out of the path name space owned by the authority, ceded to standard
use for a designated purpose.

That purpose is to facilitate discovery of information about an
origin 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 the information applies to many (or all) of the
origin's resources.

Typically, the resource(s) identified by a well-known URI will make
information about the origin (e.g., policy) available directly, or
provide references to other URIs that provide it. In general, that
information should be applicable to most origins (i.e., Web sites -
while acknowledging that some origins might not use a particular
well-known location, for various reasons).

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.

Specifically, well-known URIs are not a "protocol registry" for
applications and protocols that wish to use HTTP as a substrate.
Instead, such applications and protocols are encouraged to used an
absolute 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

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/", 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 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]. This means they cannot contain the "/" character.

Note that this specification defines neither how to determine the
authority to use

Registered names for a particular context, nor the scope of the
metadata discovered by dereferencing the well-known URI; both should specific application SHOULD be defined by correspondingly
precise; "squatting" on generic terms is not encouraged. For
example, if the Example application itself.

Typically, wants a well-known location for
metadata, an appropriate registered name might be "example-metadata"
or even "example.com-metadata", not "metadata".

At a minimum, a registration will reference a specification that
defines the format and associated media type to be obtained by
dereferencing the well-known URI. URI, along with the URI scheme(s) that
the well-known URI can be used with. If no URI schemes are
explicitly specified, "HTTP" and "HTTPS" are assumed.

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 [RFC7231] method handling).

Note that this specification defines neither how to determine the
hostname to use to find the well-known URI for a particular
application, nor the scope of the metadata discovered by
dereferencing the well-known URI; both should be defined by the
application itself.

Also, 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.

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.

See also Section 4 for Security Considerations

This memo does not specify regarding well-known
locations.

3.1. Registering Well-Known URIs

The "Well-Known URIs" registry is located at
"https://www.iana.org/assignments/well-known-uris/". Registration
requests can be made by following the scope of applicability of metadata instructions located there or
policy obtained from a
by sending an email to the "wellknown-uri-review@ietf.org" mailing
list.

Registration requests consist of at least the following information:

URI suffix: The name requested for the well-known URI, and does 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 specify how required.

Related information: Optionally, citations to
discover additional documents
containing further relevant information.

General requirements for registered relation types are described in
Section 3.

Registrations MUST reference a freely available, stable
specification.

Note that well-known URIs can be registered by third parties
(including the expert(s)), if the expert(s) determines that an
unregistered well-known URI for is widely deployed and not likely to be
registered in a particular application. Individual
applications using this mechanism must define both aspects. timely manner otherwise. Such registrations still
are subject to the requirements defined, including the need to
reference a specification.

4. Security Considerations

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.

Security-sensitive

4.1. Interaction with the Web

In particular, applications using well-known URIs for HTTP or HTTPS
URLs need to be aware that well-known resources will be accessible to
Web browsers, and therefore is potentially able to be manipulated by
content obtained from other parts of that origin. If an attacker is
able to inject content (e.g., through a Cross-Site Scripting
vulnerability), they will be able to make potentially arbitrary
requests to the well-known resource.

HTTP and HTTPS also use origins as a security boundary for many other
mechanisms, including (but not limited to) Cookies [RFC6265], Web
Storage [W3C.REC-webstorage-20160419] and many capabilities.
Applications defining well-known locations should not assume that
they have sole access to these mechanisms.

Applications defining well-known URIs should not assume or require
that they are the only application using the origin, since this is a
common deployment pattern; instead, they should use appropriate
mechanisms to mitigate the risks of co-existing with Web
applications, such as (but not limited to):

o Using Strict Transport Security [RFC6797] to assure that HTTPS is
used

o Using Content-Security-Policy [W3C.WD-CSP3-20160913] to constrain
the capabilities of content, thereby mitigating Cross-Site
Scripting attacks (which are possible if client-provided data is
exposed in any part of a response in the application)

o Using X-Frame-Options [RFC7034] to prevent content from being
included in a HTML frame from another origin, thereby enabling
"clickjacking"

o Using Referrer-Policy [W3C.CR-referrer-policy-20170126] to prevent
sensitive data in URLs from being leaked in the Referer request
header

o Using the 'HttpOnly' flag on Cookies to assure that cookies are
not exposed to browser scripting languages [RFC6265]

4.2. Scoping Applications

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; if this is not specified, security issues can arise from
implementation deviations and confusion about boundaries between
applications.

Applying metadata discovered in a well-known URI to resources other
than those co-located on the same origin risks administrative as well
as security issues. For example, allowing
"https://example.com/.well-known/example" to apply policy to
"https://department.example.com", "https://www.example.com" or even
"https://www.example.com:8000" assumes a relationship between hosts
where there may be none, or there may be conflicting motivations.

4.3. Hidden Capabilities

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 .well-
known directory, they would be able to control its contents, possibly
without the administrator realising it.

5. IANA Considerations

5.1. The Well-Known URI Registry

This document specifies specification updates the registration procedures for the well-known URI "Well-
Known URI" registry, first defined in [RFC5785]. [RFC5785]; see Section 3.1.

Well-known URIs are registered on the advice of one or more experts
(appointed by the IESG or their delegate), with a Specification
Required (using terminology from [RFC8126]).

To allow for the allocation of values prior to publication, the
expert(s) may approve

The Experts' primary considerations in evaluating registration once they are satisfied that such
a specification will be published.

Registration
requests can be sent are: * Conformance to the wellknown-uri-
review@ietf.org mailing list for review requirements in Section 3 * The
availability and comment, with an
appropriate subject (e.g., "Request for well-known URI: example").

5.1.1. Registration Template

URI suffix: stability of the specifying document * The name requested for security
considerations outlined in Section 4

IANA will direct any incoming requests regarding the well-known URI, relative registry to
"/.well-known/"; e.g., "example".

Change controller: For Standards-Track RFCs, state "IETF". For
others, give this
document and, if defined, the name of processes established by the responsible party. Other details
(e.g., postal address, e-mail address, home page URI) may also be
included.

Specification document(s): Reference expert(s);
typically, this will mean referring them to the document that specifies
the field, preferably including a URI registry Web page.

IANA should replace all references to RFC 5988 in that can be used registry have
been replaced with references to retrieve
a copy of the this 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,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.

[RFC5741] Daigle, L., Ed., Kolkman, O., Ed., and IAB, "RFC Streams,
Headers, and Boilerplates", RFC 5741,
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>.

[RFC7320] Nottingham, M., "URI Design and Ownership", BCP 190,
RFC 7320, DOI 10.17487/RFC7320, July 2014,
<https://www.rfc-editor.org/info/rfc7320>.

[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.

6.2. Informative References

[RFC4918] Dusseault, L., Ed., "HTTP Extensions for Web Distributed
Authoring and Versioning (WebDAV)", RFC 4918,
DOI 10.17487/RFC4918, June 2007,
<https://www.rfc-editor.org/info/rfc4918>.

[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785,
DOI 10.17487/RFC5785, April 2010,
<https://www.rfc-editor.org/info/rfc5785>.

[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>.

[RFC6797] Hodges, J., Jackson, C., and A. Barth, "HTTP Strict
Transport Security (HSTS)", RFC 6797,
DOI 10.17487/RFC6797, November 2012,
<https://www.rfc-editor.org/info/rfc6797>.

[RFC7034] Ross, D. and T. Gondrom, "HTTP Header Field X-Frame-
Options", RFC 7034, DOI 10.17487/RFC7034, October 2013,
<https://www.rfc-editor.org/info/rfc7034>.

[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.

[W3C.CR-referrer-policy-20170126]
Eisinger, J. and E. Stark, "Referrer Policy", World Wide
Web Consortium CR CR-referrer-policy-20170126, January
2017,
<https://www.w3.org/TR/2017/CR-referrer-policy-20170126>.

[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

[W3C.REC-webstorage-20160419]
Hickson, I., "Web Storage (Second Edition)", World Wide
Web, Volume One",
Web Consortium Recommendation REC-webstorage-20160419,
April 2016,
<http://www.w3.org/TR/2016/REC-webstorage-20160419>.

[W3C.WD-CSP3-20160913]
West, M., "Content Security Policy Level 3", World Wide
Web Consortium
Recommendation REC-webarch-20041215, December 2004,
<http://www.w3.org/TR/2004/REC-webarch-20041215>. WD WD-CSP3-20160913, September 2016,
<https://www.w3.org/TR/2016/WD-CSP3-20160913>.

6.3. URIs

[1] https://github.com/mnot/I-D/labels/rfc5785bis

[2] https://mnot.github.io/I-D/rfc5785bis/

[3] https://github.com/mnot/I-D/commits/gh-pages/rfc5785bis

[4] https://datatracker.ietf.org/doc/draft-nottingham-rfc5785bis/

[5] http://www.robotstxt.org/

Appendix A. 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 sometimes necessary. 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".

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

o Discuss appropriate and inappropriate uses more fully Allow non-Web well-known locations

o Adjust IANA instructions

o Update references

o Various other clarifications

Author's Address

Mark Nottingham

Email: mnot@mnot.net
URI: https://www.mnot.net/