SAML was initially a standard for cross-domain SSO. A user who is logged on to the domain * could transparently point his browser to a web application in another domain * without having to authenticate again. His identity (and other attributes) are passed on transparently, behind the scenes. Many mechanisms were defined to exchange the information contained in SAML token (signed XML structures) between an Identity Provider and a Relying Party, including SOAP very early on (the SAML SOAP Binding).

But SAML was taken further. WS-Security SAML Token Profile allows the use of SAML tokens in SOAP messages secured with WS-Security. And WS-Trust and its Secure Token Service standardized the mechanism to obtain or exchange SAML (or other) tokens.

The STS is a standard (web) service to obtain such a SAML token: 1) through standard authentication mechanisms or 2) by exchanging one token for another (SAML to SAML, non-SAML to SAML or SAML to non-SAML).

But transferring SAML tokens between domains means the exchange of information between heterogeneous organizations. The SAML standard does not define how attributes within the SAML tokens should be named nor what their content should exactly look like. Every organziation is free to specify how information is structured in a SAML token:

  • what information or attributes is contained in the SAML token: name, cost center, department, …
  • how the atrributes should are named, e.g. LastName or lname?
  • how the information in the attributes is represented

Imagine a vendors of office materials (Staples) that wants to offer a SSO experience to the employees of its majore customers. If every customer (large enterprises themselves) use a different SAML token structure, the office material vendor will have a great time translating the information from these different SAML tokens to its own attributes. And what if information is missing in the SAML token, e.g. what is the maximum value that employee may purchase?

Another integration challenge!

Note: Microsoft prefers the use of the term claim

Authored by: Guy