Network Working Group P. Saint-Andre
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track May 1, 2013
Expires: November 2, 2013
The 'acct' URI Scheme
draft-ietf-appsawg-acct-uri-04
Abstract
This document defines the 'acct' Uniform Resource Identifier (URI)
scheme as a way to identify a user's account at a service provider,
irrespective of the particular protocols that can be used to interact
with the account.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Definition . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
Existing Uniform Resource Identifier (URI) schemes that enable
interaction with, or that identify resources associated with, a
user's account at a service provider are tied to particular services
or application protocols. Two examples are the 'mailto' scheme
(which enables interaction with a user's email account) and the
'http' scheme (which enables retrieval of web files controlled by a
user or interaction with interfaces providing information about a
user). However, there exists no URI scheme that generically
identifies a user's account at a service provider without specifying
a particular protocol to use when interacting with the account. This
specification fills that gap.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
3. Rationale
During formalization of the WebFinger protocol
[I-D.ietf-appsawg-webfinger], much discussion occurred regarding the
appropriate URI scheme to include when specifying a user's account as
a web link [RFC5988]. Although both the 'mailto' [RFC6068] and
'http' [RFC2616] schemes were proposed, not all service providers
offer email services or web interfaces on behalf of user accounts
(e.g., a microblogging or instant messaging provider might not offer
email services, or an enterprise might not offer HTTP interfaces to
information about its employees). Therefore, the participants in the
discussion recognized that it would be helpful to define a URI scheme
that could be used to generically identify a user's account at a
service provider, irrespective of the particular application
protocols used to interact with the account. The result was the
'acct' URI scheme defined in this document.
(Note that a user is not necessarily a human; it could be an
automated application such as a bot, a role-based alias, etc.
However, an 'acct' URI is always used to identify something that has
an account at a service, not the service itself.)
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4. Definition
The syntax of the 'acct' URI scheme is defined under Section 5 of
this document. Although 'acct' URIs take the form "user@host", the
scheme is designed for the purpose of identification instead of
interaction (regarding this distinction, see Section 1.2.2 of
[RFC3986]). The "Internet resource" identified by an 'acct' URI is a
user's account hosted at a service provider, where the service
provider is typically associated with a DNS domain name. Thus a
particular 'acct' URI is formed by setting the "user" portion to the
user's account name at the service provider and by setting the "host"
portion to the DNS domain name of the service provider.
Consider the case of a user with an account name of "foobar" on a
microblogging service "status.example.net". It is taken as
convention that the string "foobar@status.example.net" designates
that account. This is expressed as a URI using the 'acct' scheme as
"acct:foobar@status.example.net".
It is not assumed that an entity will necessarily be able to interact
with a user's account using any particular application protocol, such
as email; to enable such interaction, an entity would need to use the
appropriate URI scheme for such a protocol, such as the 'mailto'
scheme. While it might be true that the 'acct' URI minus the scheme
name (e.g., "user@example.com" derived from "acct:user@example.com")
can be reached via email or some other application protocol, that
fact would be purely contingent and dependent upon the deployment
practices of the provider.
Because an 'acct' URI enables abstract identification only and not
interaction, this specification provides no method for dereferencing
an 'acct' URI on its own, e.g., as the value of the 'href' attribute
of an HTML anchor element. For example, there is no behavior
specified in this document for an 'acct' URI used as follows:
find out more
Instead, an 'acct' URI is employed indirectly and typically is passed
around as a parameter in the background within a protocol flow so
that an entity can interact with a resource related to that
identified by the 'acct' URI in a particular way or for a particular
purpose. For example, in the WebFinger protocol
[I-D.ietf-appsawg-webfinger] an 'acct' URI is used to identify the
resource about which an entity would like to discover metadata
expressed as "web links" [RFC5988]; the relevant HTTP request passes
an 'acct' URI (or some other URI) as the value of a "resource"
parameter, as shown in the following example:
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GET /.well-known/webfinger?resource=acct%3Abob%40example.com HTTP/1.1
Therefore, any protocol that uses 'acct' URIs, such as the WebFinger
protocol [I-D.ietf-appsawg-webfinger] or the Simple Web Discovery
protocol [I-D.jones-simple-web-discovery], is responsible for
specifying how an 'acct' URI is employed in the context of that
protocol (in particular, how it is dereferenced or resolved; see
[RFC3986]). As a concrete example, in the WebFinger protocol an
'acct' URI is passed as a parameter in an HTTP request for metadata
(i.e., web links) about the resource; the service retrieves the
metadata associated with the account identified by that URI and then
provides that metadata to the requesting entity in an HTTP response
(see [I-D.ietf-appsawg-webfinger] for details). Similar
functionality is envisioned for other uses of 'acct' URIs.
If an application needs to compare two 'acct' URIs (e.g., for
purposes of authentication and authorization), it MUST do so using
case normalization and percent-encoding normalization as specified in
Sections 6.2.2.1 and 6.2.2.2 of [RFC3986].
5. IANA Considerations
In accordance with the guidelines and registration procedures for new
URI schemes [RFC4395], this section provides the information needed
to register the 'acct' URI scheme.
5.1. URI Scheme Name
acct
5.2. Status
permanent
5.3. URI Scheme Syntax
The 'acct' URI syntax is defined here in Augmented Backus-Naur Form
(ABNF) [RFC5234], borrowing the 'host', 'pct-encoded', 'sub-delims',
'unreserved' rules from [RFC3986]:
acctURI = "acct" ":" userpart "@" host
userpart = unreserved / sub-delims
0*( unreserved / pct-encoded / sub-delims )
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5.4. URI Scheme Semantics
The 'acct' URI scheme identifies accounts hosted at service
providers. It is used only for identification, not interaction. A
protocol that employs the 'acct' URI scheme is responsible for
specifying how an 'acct' URI is dereferenced in the context of that
protocol. There is no media type associated with the 'acct' URI
scheme.
5.5. Encoding Considerations
As specified in [RFC3986], the 'acct' URI scheme allows any character
from the Unicode repertoire [UNICODE] encoded as UTF-8 [RFC3629] and
then percent-encoded into valid ASCII [RFC20]. Note that domain
labels need to be encoded as A-labels (see [RFC5890]) in order to
support internationalized domain names (IDNs).
5.6. Applications/Protocols That Use This URI Scheme Name
At the time of this writing, only the WebFinger protocol uses the
'acct' URI scheme. However, use is not restricted to the WebFinger
protocol, and the scheme might be considered for use in other
protocols, such as Simple Web Discovery.
5.7. Interoperability Considerations
There are no known interoperability concerns related to use of the
'acct' URI scheme.
5.8. Security Considerations
See Section 5 of RFC XXXX. [Note to RFC Editor: please replace XXXX
with the number issued to this document.]
5.9. Contact
Peter Saint-Andre, psaintan@cisco.com
5.10. Author/Change Controller
This scheme is registered under the IETF tree. As such, the IETF
maintains change control.
5.11. References
None.
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6. Security Considerations
Because the 'acct' URI scheme does not directly enable interaction
with a user's account at a service provider, direct security concerns
are minimized.
However, an 'acct' URI does provide proof of existence of the
account; this implies that harvesting published 'acct' URIs could
prove useful to spammers and similar attackers, for example if they
can use an 'acct' URI to leverage more information about the account
(e.g., via WebFinger) or if they can interact with protocol-specific
URIs (such as 'mailto' URIs) whose user@host portion is the same as
that of the 'acct' URI.
In addition, protocols that make use of 'acct' URIs are responsible
for defining security considerations related to such usage, e.g., the
risks involved in dereferencing an 'acct' URI, the authentication and
authorization methods that could be used to control access to
personal data associated with a user's account at a service, and
methods for ensuring the confidentiality of such information.
The use of percent-encoding allows a wider range of characters in
account names, but introduces some additional risks. Implementers
are advised to disallow percent-encoded characters or sequences that
would (1) result in space, null, control, or other characters that
are otherwise forbidden, (2) allow unauthorized access to private
data, or (3) lead to other security vulnerabilities.
7. References
7.1. 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.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.
7.2. Informative References
[I-D.ietf-appsawg-webfinger]
Jones, P., Salgueiro, G., and J. Smarr, "WebFinger",
draft-ietf-appsawg-webfinger-13 (work in progress),
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April 2013.
[I-D.jones-simple-web-discovery]
Jones, M. and Y. Goland, "Simple Web Discovery (SWD)",
draft-jones-simple-web-discovery-04 (work in progress),
November 2012.
[RFC20] Cerf, V., "ASCII format for network interchange", RFC 20,
October 1969.
[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.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI Schemes", BCP 35,
RFC 4395, February 2006.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, August 2010.
[RFC5988] Nottingham, M., "Web Linking", RFC 5988, October 2010.
[RFC6068] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto'
URI Scheme", RFC 6068, October 2010.
[UNICODE] The Unicode Consortium, "The Unicode Standard, Version
6.1", 2012,
.
Appendix A. Acknowledgements
The 'acct' URI scheme was originally proposed during work on the
WebFinger protocol; special thanks are due to Blaine Cook, Brad
Fitzpatrick, and Eran Hammer-Lahav for their early work on the
concept (which in turn was partially inspired by work on Extensible
Resource Indentifiers at OASIS). The scheme was first formally
specified in [I-D.ietf-appsawg-webfinger]; the authors of that
specification (Paul Jones, Gonzalo Salgueiro, and Joseph Smarr) are
gratefully acknowledged. Thanks are also due to Melvin Carvalho,
Martin Duerst, Graham Klyne, Barry Leiba, Subramanian Moonesamy, Evan
Prodromou, James Snell, and other participants in the IETF APPSAWG
for their feedback. Meral Shirazipour completed a Gen-ART review.
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Dave Cridland completed an AppsDir review, and is gratefully
acknowledged for providing proposed text that was incorporated into
Section 3 and Section 5. IESG comments from Richard Barnes, Adrian
Farrel, Stephen Farrell, Pete Resnick, and Sean Turner also led to
improvements in the specification.
Author's Address
Peter Saint-Andre
Cisco Systems, Inc.
1899 Wynkoop Street, Suite 600
Denver, CO 80202
USA
Email: psaintan@cisco.com
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