Network Working Group                                     P. Saint-Andre
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                           June 17, 2013
Expires: December 19, 2013

                         The 'acct' URI Scheme


   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  . . . . . . . . . . . . . . . . . . 8
   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",
   "OPTIONAL" in this document are to be interpreted as described in

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 "".  It is taken as
   convention that the string "" designates
   that account.  This is expressed as a URI using the 'acct' scheme as

   A common scenario is for a user to register with a service provider
   using an identifier (such as an email address) that is associated
   with some other service provider.  For example, a user with the email
   address "juliet@capulet.example" might register with a commerce
   website whose domain name is "shoppingsite.example".  In order to use
   her email address as the localpart of the 'acct' URI, the at-sign
   character (U+0040) needs to be percent-encoded as described in
   [RFC3986].  Thus the resulting 'acct' URI would be

   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., "" derived from "")
   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:

   <a href=''>find out more</a>

   Instead, an 'acct' URI is employed indirectly and typically is passed

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   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:

   GET /.well-known/webfinger? 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 and 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


5.2.  Status


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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 )

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

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,

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5.10.  Author/Change Controller

   This scheme is registered under the IETF tree.  As such, the IETF
   maintains change control.

5.11.  References


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,

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              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

              Jones, P., Salgueiro, G., and J. Smarr, "WebFinger",
              draft-ietf-appsawg-webfinger-14 (work in progress),
              May 2013.

              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

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   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.
   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, Barry Leiba, 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


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