Liberty Identity Federation Framework

The Liberty Identity Federation Framework (Liberty ID-FF) defines a set of protocols, bindings, and profiles that provides a solution for identity federation, cross-domain authentication, and session management. This framework can be used to create a new identity management system or to develop one in conjunction with legacy systems. This section contains information regarding the Liberty ID-FF.

• The Liberty ID-FF Model

• The Liberty ID-FF Convergence

• Liberty ID-FF Protocols and Schema

• Liberty ID-FF Bindings and Profiles

• Additional Liberty ID-FF Documents

More detailed information about the Liberty ID-FF 1.2 specifications can be found on the Liberty Alliance Project web site at the Liberty Alliance ID-FF 1.2 Specifications page.

The Liberty ID-FF Model

The Liberty ID-FF is designed to work with heterogeneous platforms, various networking devices (including personal computers, mobile phones, and personal digital assistants), and emerging technologies. The following figure shows the subjects involved in a Liberty ID-FF implementation.

Figure 1–1 Subjects Involved in a Liberty ID-FF Implementation

• A principal can have a defined local identity with more than one provider, and it has the option to federate the local identities. The principal might be an individual user, a group of individuals, a corporation, or a component of the Liberty architecture.

• A service provider is a commercial or not-for-profit organization that offers a web-based service such as a news portal, a financial repository, or retail outlet.

• An identity provider is a service provider that stores identity profiles and offers incentives to other service providers for the prerogative of federating their user identities. Identity providers might also offer services above and beyond those related to identity profile storage.

• To support identity federation, all service providers and identity providers must join together into a circle of trust. A circle of trust must contain at least one identity provider and at least two service providers. (One organization may be both an identity provider and a service provider.) Providers in a circle of trust must first write operational agreements to define their relationships. An operational agreement is a contract between organizations that defines how the circle will work. For more information, see Concept of Trust.

The Liberty ID-FF Convergence

Up to version 1.1, the Liberty ID-FF was developed using the SAML 1.0 specification. The Liberty ID-FF 1.2 was then developed using the SAML 1.1 specification. Following the release of version 1.2, the Liberty ID-FF was reintroduced into the SAML 2.0 specification. Additionally, SAML 2.0 adds components of the Shibboleth initiative. Going forward, SAML 2.0 will be the basis on which the Liberty Alliance Project builds additional federated identity applications (such as web service-enabled permissions-based attribute sharing). As such, SAML 2.0 is a critical step towards full convergence of federated identity standards. The following diagram illustrates the convergence history of SAML and the Liberty ID-FF.

Figure 1–2 Liberty ID-FF and SAML Convergence

For more information on this convergence (including how the Shibboleth Project was also integrated), see the Federation section of Strategic Initiatives on the Liberty Alliance Project web site.

Liberty ID-FF Protocols and Schema

The Liberty ID-FF Protocols and Schema Specifications defines transmission formats for the following functions:

• Single Sign-On and Federation Protocol

• Name Registration Protocol

• Federation Termination Notification Protocol

• Single Logout Protocol

• Name Identifier Mapping Protocol

Following are short explanations of each protocol. More detailed information can be found in the Liberty ID-FF Protocols and Schema Specifications.

Single Sign-On and Federation Protocol

The Single Sign-On and Federation Protocol defines the rules for request and response messages with which a principal is able to authenticate to one or more service providers and federate (or link) configured identities. When a principal attempts to access a service provider resource, the service provider issues a request for authentication to the principal's identity provider. The identity provider responds with a message that contains authentication information, or an artifact that points to authentication information.

Under certain conditions, an identity provider may issue an authentication response to a service provider without having received an authentication request.

The Single Sign-On and Federation Protocol also defines elements for inclusion in the request and response that control the following behaviors:

• Account federation. A principal can choose to federate a configured identity at the identity provider site with a configured identity at the service provider site.

• Account handle. An identity provider can issue an anonymous, temporary identifier to refer to a particular principal during communication with a service provider. This identifier is used to obtain information for or about the principal during federation (with the principal's consent). The account handle is generated by the identity provider during federation.

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  Note –

  This account handle is not to be confused with the handle that can be generated by the service provider after federation using the Name Registration Protocol as discussed in Name Registration Protocol.

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• Affiliation federation. Federation based on group affiliation can be enabled in an authentication request. If enabled, it indicates that the requester is acting as a member of the specified affiliation group. Federations are then established and resolved based on the affiliation, not the requesting provider. The process allows for a unique identifier that represents the affiliation.

• Authentication context. A service provider can choose the type and level of authentication that should be used when a principal logs in.

• Authentication credentials. A principal can be prompted to authenticate with a user name and password, for example, at the behest of the service provider.

• Dynamic identity provider proxying. One identity provider might be asked to authenticate a principal that has already been authenticated by a second identity provider. In this case, the first identity provider may request authentication information from the second identity provider on behalf of the service provider. Proxy behavior can be controlled by indicating a list of preferred identity providers, and a value that defines the maximum number of proxy steps that can be taken. Proxy behavior is defined locally by the proxying identity provider, although a service provider controls whether or not to proxy. For more information, see Dynamic Identity Provider Proxying.

• Identity provider introduction. When an authentication domain has more than one identity provider, a service provider can use this feature to determine which identity provider a principal is using.

• Message exchange. The authentication request defines how messages are exchanged between identity providers and service providers. The particular transfer and messaging protocol used in the exchange (such as HTTP or SOAP) are specified in profiles defined in the Liberty ID-FF Bindings and Profiles Specification. Two of these profiles are:

  • The Liberty Artifact profile relies on Security Assertion Markup Language (SAML) artifacts and assertions to relay authentication information.

  • The Liberty Browser POST profile relies on an HTML form to communicate authentication information between providers.

  See Liberty ID-FF Bindings and Profiles for more information.

• One-time federation. The ability to federate for one session only can be enabled in an authentication request. This feature is useful for service providers with no user accounts, for principals who want to act anonymously, or for dynamically created user accounts. It allows for one-time federation, rather than a one-time name identifier for a session.

Name Registration Protocol

The optional Name Registration Protocol defines the request and response messages a service provider would use to create its own opaque handle to identify a principal when communicating with the identity provider. This registration would occur after federation has been accomplished. After the service provider registers this new handle, subsequent communications with the identity provider would use this identifier rather than the identifier originally defined by the identity provider.

The handle discussed in this section is not related to the opaque handle that is generated by the identity provider during federation as defined in Single Sign-On and Federation Protocol. The Name Registration Protocol can, however, be used by the identity provider to change the opaque handle that it registered with the service provider during initial federation.

Federation Termination Notification Protocol

The Federation Termination Notification Protocol defines a one-way message that one provider would use to notify another provider when a principal has terminated identity federation. The message is asynchronous and states one of the following:

• The service provider will no longer accept authentication information regarding the particular user.

• The identity provider will no longer provide authentication information regarding the particular user.

Single Logout Protocol

The Single Logout Protocol defines the request and response messages that providers would exchange when notifying each other of logout events. This exchange would terminate all sessions when a logout occurs at either the service provider or the identity provider.

Name Identifier Mapping Protocol

The Name Identifier Mapping Protocol defines the request and response messages that one service provider can use to communicate with a second service provider to obtain the name identifier assigned to a principal federated in the name space of the second service provider. This would be used when a principal authenticated to one service provider requests access to a second service provider site with which it also has an identity federation relationship. The protocol allows the second service provider to communicate with the first service provider about the principal even though no identity federation for the principal exists between the two service providers.

Liberty ID-FF Bindings and Profiles

The Liberty ID-FF Bindings and Profiles Specification defines the bindings and profiles for the request and response messages explained in Liberty ID-FF Protocols and Schema. A binding describes how to integrate request and response messages into a transmission protocol. Currently, this specification defines only a SOAP binding. A profile defines the HTTP exchanges required to transfer the requests and responses between providers. The defined profiles are:

• Single Sign-on and Federation

• Name Identifier Registration

• Federation Termination Notification

• Single Logout

• Identity Provider Introduction

• Name Identifier Mapping

• Name Identifier Encryption

For more information about these profiles and transmission of requests and responses in general, see the Liberty ID-FF Bindings and Profiles Specification.

Additional Liberty ID-FF Documents

For additional information about the Liberty ID-FF specifications, the following documents are available on the Liberty ID-FF 1.2 specification page.

• Liberty ID-FF Architecture Overview

  Provides an architectural description of the Liberty ID-FF framework as well as policy, security, and technical notes.

• Liberty ID-FF Guidelines

  Provides guidance and checklists for implementing a Liberty-enabled environment using the Liberty ID-FF specifications.

• Liberty ID-FF Static Conformance Requirements

  Defines what features are mandatory and optional for implementations conforming to this version of the Liberty ID-FF specifications.