OpenID Attribute Exchange 1.0 - Draft 02

Abstract

OpenID Attribute Exchange is an OpenID service for exchanging identity information between endpoints. Messages for retrieval and storage of identity information are provided.

Table of Contents

1.  Terminology
    1.1.  Definitions and Conventions
2.  Overview
3.  Information Model
    3.1.  Subject Identifier
    3.2.  Attribute Name
    3.3.  Attribute Value
4.  Discovery
5.  Fetch Message
    5.1.  Fetch Request Format
    5.2.  Fetch Response Format
6.  Store Message
    6.1.  Store Request Format
    6.2.  Store Response Format
7.  Security Considerations
8.  Acknowledgements
9.  References
    9.1.  Normative References
    9.2.  Non-normative References
§  Authors' Addresses

1.  Terminology

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 [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

1.1.  Definitions and Conventions

[NOTE: Update terminology based on final OpenID 2.0 draft.]

User:

(AKA "End User" or "Subject".) A person with a digital identity who participates in OpenID based identity information exchanges using their client software, typically a web browser.

Identity Data:

A property of a digital identity in which the Property Name and Property Value are represented as a name-value pair.

Persona:

A user can have multiple personas as part of their identity. For example, a user might have a work persona and a home persona. A persona is a subset of the user's identity data.

Identity Provider:

Also called "IdP" or "Server". This is the OpenID Authentication server that a Consumer contacts for cryptographic proof that the End User owns the Claimed Identity.

Consumer:

A site that requests identity data from an Identity Provider via the user's client.

For the purposes of this document, the extension namespace identifier for the attribute exchange service will be "ax".

2.  Overview

The attribute exchange service is identified by the URI "http://openid.net/srv/ax/1.0" [NOTE: subject to change in following drafts].

An attribute is a unit of personal identity information that is identified by a unique URI. It may refer to any kind of information; see [OpenID.attribute‑properties‑1.0] (Hardt, D. and B. Ferg, “Attribute Properties for OpenID Attribute Exchange,” August 2006.) for some examples.

This service defines two additional message types for transferring attributes: fetch (see Section 5 (Fetch Message)) and store (see Section 6 (Store Message)). Fetch retrieves attribute information from an Identity Provider, while store saves or updates attribute information on the Identity Provider. Both messages originate from the Consumer site or service provider and are passed to the Identity Provider via the user agent as per the OpenID protocol specification.

The request parameters detailed here SHOULD be sent with OpenID Authentication checkid_immediate or checkid_setup requests. [NOTE: This portion of the spec will change depending on the final draft of OpenID 2.0.]

Error responses are communicated using the standard OpenID methods; see [OpenID.authentication‑2.0] (Recordon, D., Hoyt, J., and B. Fitzpatrick, “OpenID Authentication 2.0 - Draft 09,” August 2006.).

3.  Information Model

The OpenID attribute exchange service provides a mechanism for moving identity information between sites, as such its information model is simple:

An attribute is associated with a Subject Identifier

An attribute has a name and one or more values

An attribute name is of type URI

An attribute value is of type UTF-8 string [RFC3629] (Yergeau, F., “UTF-8, a transformation format of ISO 10646,” November 2003.)

3.1.  Subject Identifier

An identifier for a set of attributes. MUST be a URI.

3.2.  Attribute Name

An attribute name MUST be a URI, which is used for referring to property values.

If an attribute name URI can be resolved then it MAY be dereferenced to retrieve a description of the property.

This provides for flexibility and extensibility. Flexibility in that both URNs and URLs can be used to refer to property values. Extensibility allows any individual site, or consortium of sites, to define their own attribute names with agreements on the syntax and semantics of their associated attribute values. A set of attributes has been defined in [OpenID.attribute‑properties‑1.0] (Hardt, D. and B. Ferg, “Attribute Properties for OpenID Attribute Exchange,” August 2006.).

3.3.  Attribute Value

A attribute value MUST be a UTF-8 string and can optionally have no value, a single value or multiple values. For example Beth might have multiple home email addresses: beth@home.com and beth.surname@home.com.

4.  Discovery

Discovery of the attribute exchange service is achieved via the mechanism described in [OpenID.authentication‑2.0] (Recordon, D., Hoyt, J., and B. Fitzpatrick, “OpenID Authentication 2.0 - Draft 09,” August 2006.). The attribute exchange namespace "http://openid.net/srv/ax/1.0" SHOULD be listed as an <xrd:Type> child element of the <xrd:Service> element in the XRDS discovery document.

5.  Fetch Message

The fetch message is used to retrieve personal identity attributes from an Identity Provider.

5.1.  Fetch Request Format

All of the following request fields are OPTIONAL, though at least one of "openid.ax.required" or "openid.ax.if_available" MUST be specified in the request.

Separate "required" or "if_available" directives must be used for each identifier name referred to. Any identifier name referred to in a "required" or "if_available" parameter MUST have an associated "openid.ax.fetch.<identifier name>" parameter.

Only one "update_url" parameter may be specified.

openid.ax.fetch.<identifier name>

Associates an identifier name with the attribute URI which is the value of this parameter. The name will be used as the lvalue in the fetch response message.

openid.ax.required

The value of this parameter is an identifier name corresponding to a URI defined in an "openid.ax.fetch.<identifier name>". The Identity Provider must provide the identity information specified in this parameter or return an error condition.

openid.ax.if_available

The value of this parameter is an identifier name corresponding to a URI defined in an "openid.ax.fetch.<identifier name>". The Identity Provider may provide the identity information specified in this parameter. Not including the information in the response does not constitute an error condition.

openid.ax.update_url

If this URL is specified, the Identity Provider may re-post the fetch response data to it at some time after the initial response has been sent. This "unsolicited" response message would be generated in response to an attribute information update, and would contain the updated data. The relying party may include transaction data encoded in the URL such that it contains enough information to match the attribute information to the identity subject. Additional information may be encoded in the URL by the relying party as necessary. If the Identity Provider supports this feature it MUST return the parameter as part of the fetch response message. If it does not support this feature it may legally ignore this parameter.

This example requests the required full name information, and the optional favourite dog information.

openid.ns.ax=http://openid.net/srv/ax/1.0
openid.ax.fetch.fname=http://example.com/schema/fullname
openid.ax.fetch.fav_dog=http://example.com/schema/favourite_dog
openid.ax.required=fname
openid.ax.if_available=fav_dog
openid.ax.update_url=http://idconsumer.com/update?transaction_id=a6b5c41

5.2.  Fetch Response Format

The fetch response message supplies the information requested in the fetch request in a format suitable for consumption by a standard HTML form processor. Each attribute is supplied with the assigned identifier name as the lvalue and the attribute value as the rvalue.

A fetch response message may also be sent to the "update_url" specified in Section 5.1 (Fetch Request Format) in response to attribute value updates on the Identity Provider.

If the Identity Provider receives an "update_url" parameter and it intends to support the attribute update feature, it MUST present the "update_url" parameter and value as part of the fetch response message.

The response to the previous request example, in which the required full name information and the optional favourite dog information are both supplied.

fname="John Smith"
fav_dog="Spot"
update_url=http://idconsumer.com/update?transaction_id=a6b5c41

6.  Store Message

The store message is used to store personal identity information to the Identity Provider.

6.1.  Store Request Format

All of the following request fields are OPTIONAL. Any identifier name referred to in a "value" parameter MUST have an associated "openid.ax.label.<identifier name>" parameter.

openid.ax.label.<identifier name>

Associates an identifier name with the attribute URI which is the value of this parameter. The name will be used as a reference in an "openid.ax.value.<identifier name>" parameter.

openid.ax.value.<identifier name>

Assigns a value to the identifier with the name assigned by a "label" parameter.

openid.ns.ax=http://openid.net/srv/ax/1.0
openid.ax.label.fname=http://example.com/schema/fullname
openid.ax.value.fname="Bob Smith"

6.2.  Store Response Format

The store response consists of an empty response message with the 200 HTTP response code as per the OpenID specification [OpenID.authentication‑2.0] (Recordon, D., Hoyt, J., and B. Fitzpatrick, “OpenID Authentication 2.0 - Draft 09,” August 2006.).

7.  Security Considerations

[NOTE: TBD]

8.  Acknowledgements

John Merrels and other contributors to the document 'draft-merrels-dix'. Portions of that document were re-used for this one.

9.  References

9.1. Normative References

9.2. Non-normative References

Authors' Addresses