Business is becoming increasingly virtual and decentralized, while real-time management of relationships with employees, contractors, partners, suppliers, and customers is becoming ever more crucial. Even within a single company, applications may reside on different platforms, in separate departmental security domains, in legacy databases derived from prior acquisitions, or (thanks to outsourcing) in separate companies. As gaining access to distributed resources becomes increasingly vital, the ability to manage identity effectively becomes a paramount concern.

Federated Identity
"Federated Identity" is a set of mechanisms through which companies can share identity information between security domains. As a result of federation, companies are now able to create identity-based applications (such as federated single sign-on) that enable increased access to cross-boundary information.

Federated identity delivers several compelling benefits to organizations. Federation means that local identities and their associated data stay in place, but they are linked together through higher-level mechanisms. In addition, federated identity organizes controlled linkages among the distributed identities of a user. This allows for efficient management, control, and movement in a radically distributed world. As organizations integrate more tightly with trading partners and outsourcers, federated identity provides a flexible mechanism that authenticates users from partner organizations and provides them with seamless access to protected online resources.

But federated identity and the standards surrounding it can be very confusing. From Liberty to WS-* to SAML and sea to shining sea, federation has become a bit of a tangle. This article will sort through some of the acronym jungle.

The Beginning of Federated Identity Standards
The move for federated identity standards began because customers of enterprise identity management companies started to ask how they could obtain single sign-on to and from their partner organizations. The fact that vendors could not ensure their own systems would achieve ubiquity of deployment led vendors to quickly realize that the ultimate solution to this problem was not one-off integration, but rather a standard mechanism for single sign-on.

The quest for developing one standard began with a company named Securant. (Securant and their identity management platform, "ClearTrust," was later sold to RSA Security). Securant worked for several months - with a few dozen of its customers, partners, and other vendors - to create a standard called "AuthXML." A few days after AuthXML was publicly announced, Netegrity and VeriSign announced their own standardization effort for the same problem - "S2ML." Through the encouragement of customers and analysts, it was decided that it was best for all involved if the efforts were combined.

During this time, a couple of meetings were held with representatives of all of the leading Web access control vendors. Ultimately, it was decided to merge the two standards efforts at the OASIS standards organization. All of the members of that group joined OASIS to work on the new standard, which took its name from the two standards it was based on, and was named SAML (the "Security Assertion Markup Language"). Their work resulted in the SAML specification, released on January 9, 2001.

From SAML to Liberty to WS Federation
The Liberty Alliance, a consortium of technology vendors and end-user companies, was formed to provide an open standard for federated identity. Liberty's work sought to build upon SAML to provide, in essence, an extension that more tightly defined the broad-based work that SAML had started. In so doing, Liberty also incorporated the WS-Security specification that Microsoft, IBM (and others) had submitted to the OASIS body. And, of course, the story doesn't end there.

Microsoft, IBM, VeriSign, and others united to write a broad set of specifications under the "WS" label. This body of work is intended to be a more modular architecture than other federated identity specifications - primarily because the WS work is meant to include other Web services needs. Accordingly, one can find WS-Security, Policy, Trust, Secure Conversation, and WS-Federation - where federation is one member of a larger family.

This tangle of standards and dependencies leads us to a brief explanation of the federated identity standards universe.

The Universe of Federated Identity
The universe of federated identity has come to encompass much more than simply single sign-on. Groups like the Liberty Alliance and the vendors focused on the WS-Federation specifications have begun to work on attribute exchange and associated services.

Figure 1 outlines the standards and dependencies that exist today. A brief explanation of each follows.

SAML 1.0, 1.1, and 2.0
SAML pronounced "Sam -el" is an extensible language for securely exchanging user information between security domains. SAML 1.0 defines a security token format (called an assertion), as well as "profiles" that define methods of using these assertions to provide Web single sign-on. SAML 1.1 incorporates feedback and errata from the 1.0 specification. SAML 2.0 is currently in the solution proposal phase - a state meant to address the requirements outlined in the market requirements document. SAML 2.0's primary objective is an incorporation of Liberty ID-FF 1.2, which I will discuss later.

Liberty Phase 1 (ID-FF 1.0)
Liberty Phase 1 extends SAML 1.0 by adding its own profiles for how to wield SAML assertions. These additional profiles add support for account linking, identity provider introduction, and global logout. The Liberty Alliance model defines roles within a federation - an Identity Provider (IdP) and a Service Provider (SP). Liberty ID-FF1.1 incorporates feedback and errata from the 1.0 specification.

Liberty Phase 2 (ID-FF 1.2)
This set of standards extends ID-FF with new functionality, such as one-time assertions of identity (for anonymity), metadata exchange, and affiliate relationships. Liberty Phase 2 (ID-WSF 1.0) is a set of standards that extend the existing Liberty framework with functionality for discovering and offering identity-related services. Profile access mechanisms are specified as an initial service, allowing for access to user attributes. Liberty Phase 2 defines many of its messages and protocol bindings in terms of SAML 1.1, and uses WS-Security for securing SOAP messages.

Liberty Phase 3
This set of standards still in the elaboration stage, but it is expected that ID-WSF will be extended with new services built on top of attribute exchange, such as a digital wallet and calendaring/address book services.

WS-Security
This specification defines mechanisms for providing security token-based integrity and confidentiality on Web Service (SOAP) messages. Several security tokens are defined, as well as a mechanism for associating them with messages.

WS-Security Extensions (WS-Trust, WS-Policy, WS-Federation)
This collection of specifications is an evolving set of Web service-oriented mechanisms for layering authentication, authorization, and policy across both a single and multiple security domains. WS-Federation defines a framework for federation. Profiles will be developed subsequently to specify the details for implementation.

OASIS WSS
An Oasis technical committee focused on the finishing stages of standardizing WS-Security and several security token types.

Practically Speaking
Confused? Of course you are - that's why this article exists. To sort this out, let's deal with the universe of federation standards as they exist today. That leaves us with SAML 1.1 (which is not backward compatible with SAML 1.0), Liberty 1.1, and Liberty Phase 2.

Given all of the above, the distinguishing factor is simple:

If you are an enterprise that is seeking to link two pre-existing accounts, and you must do so before the end of Q1 2005, then your easiest path is to use the Liberty Alliance specifications.

The reason for this is simple. While SAML 1.1 will allow you to perform the same operations, it will require you to extend the profiles to do so. The Liberty Alliance - in its current form - is built to accomplish this operation. That said, all of this will change as SAML 2.0 is released (realistically it should ship in products in the Q2 2005 timeframe), as SAML 2.0 will incorporate Liberty 1.2.

The Future of Federated Identity Standards
The one question that surfaces time and time again is around convergence - will there be a convergence of the federated identity standards? Hopefully, this article has shone some light on that conundrum. SAML and Liberty are becoming increasingly intertwined. WS-Federation (and the supporting specifications) stand apart. Broadly speaking, then, federated identity sits in two camps: the SAML/Liberty camp and the WS-Federation camp. Of course, some vendors are planning to incorporate all standards.

In the meantime, the practical implementation of federated identity becomes a question of business drivers. If there is a business imperative to more tightly integrate and manage distributed systems of identity, and that business imperative demands some near-term action, then the enterprise needs to make some hard choices. The safe bet is a vendor that has stated support for all three standards (nearly all do). The implementation choices will most likely come down to the use case - and if that use case is about linking two pre-existing accounts, then the Liberty Alliance presents the easiest path.