OpenID Attribute Exchange 1.0 - Draft 03

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 Type Identifier
    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
        6.2.1.  Storage Success
        6.2.2.  Storage Failure
7.  Security Considerations
8.  Acknowledgements
9.  References
    9.1.  Normative References
    9.2.  Non-normative References
§  Author's Address

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]. This URI must be specified in the extension namespace declaration.

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‑types‑1.0] (Hardt, D., “OpenID Attribute Types - Draft 02,” November 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., Fitzpatrick, B., and D. Hardt, “OpenID Authentication 2.0 - Draft 10,” 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 type identfier and a value

An attribute type identifier is a URI

An attribute value is a 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. The subject identifier corresponds to the end-user identifier in the authentication portion of the messages. In other words, the subject of the identity attributes in the attribute exchange part of the message is the same as the end-user in the authentication part. The subject identifier is not included in the attribute exchange.

3.2.  Attribute Type Identifier

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

If an attribute type identifier 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 types with agreements on the syntax and semantics of their associated attribute values. The process for defining new attribute types is defined in [OpenID.attribute‑types‑1.0] (Hardt, D., “OpenID Attribute Types - Draft 02,” November 2006.).

3.3.  Attribute Value

A attribute value MUST be a UTF-8 string and may optionally have no value.

4.  Discovery

Discovery of the attribute exchange service is achieved via the mechanism described in [OpenID.authentication‑2.0] (Recordon, D., Hoyt, J., Fitzpatrick, B., and D. Hardt, “OpenID Authentication 2.0 - Draft 10,” 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.

Multiple aliases in the "required" or "if_available" directives are separated with a comma, ",". Any alias referred to in a "required" or "if_available" parameter MUST have an associated "openid.ax.fetch.<alias>" parameter.

openid.ax.fetch.<alias>

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

openid.ax.required

The value of this parameter is an alias corresponding to a URI defined in an "openid.ax.fetch.<alias>". The Identity Provider must provide the identity information specified in this parameter or return an error condition. Multiple aliases are separated with a comma, ",".

openid.ax.if_available

The value of this parameter is an alias corresponding to a URI defined in an "openid.ax.fetch.<alias>". 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. Multiple aliases are separated with a comma, ",".

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 and gender 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.gender=http://example.com/schema/gender
openid.ax.fetch.fav_dog=http://example.com/schema/favourite_dog
openid.ax.required=fname,gender
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. Each attribute is supplied with the assigned alias prefixed by "openid.ax.value" as the lvalue and the attribute value as the rvalue. Attribute types are also returned in the "type" parameter.

All requested values are returned back. If the value was not supplied or available from the user, it will be returned as an empty value. This enables the RP to know that the IdP did process the request.

openid.ax.type.<alias>

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

openid.ax.value.<alias>

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

openid.ax.update_url

Returns the "update_url" parameter specified in the request. 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.

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.

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

openid.ns.ax=http://openid.net/srv/ax/1.0
openid.ax.type.fname=http://example.com/schema/fullname
openid.ax.type.gender=http://example.com/schema/gender
openid.ax.type.fav_dog=http://example.com/schema/favourite_dog
openid.ax.value.fname=John Smith
openid.ax.value.gender=M
openid.ax.value.fav_dog=Spot
openid.ax.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 alias referred to in a "value" parameter MUST have an associated "openid.ax.type.<alias>" parameter.

openid.ax.type.<alias>

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

openid.ax.value.<alias>

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

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

6.2.  Store Response Format

6.2.1.  Storage Success

The successful store response consists of a successful response message with the 200 HTTP response code as per the OpenID specification [OpenID.authentication‑2.0] (Recordon, D., Hoyt, J., Fitzpatrick, B., and D. Hardt, “OpenID Authentication 2.0 - Draft 10,” August 2006.). No additional parameters are sent.

6.2.2.  Storage Failure

If the store request fails, a parameter named "status" MUST be sent with the value "failure".

Implementations MAY send an additional parameter, "status.description", containing a brief explanation of the error response.

openid.ax.status

On storage failure, the status parameter is sent with the value "failure".

openid.ax.status.description

Optional parameter describing the error condition leading to the failure response.

openid.ns.ax=http://openid.net/srv/ax/1.0
openid.ax.status=failure
openid.ax.status.description=General storage failure

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

Author's Address