SAML, WS-Security and the Secure Token Service of WS-Trust result in a very interesting mix, where federated identity and integration (web services) come together.
Microsoft has published the free book(let) "A Guide to Claims–based Identity and Access Control". Obviously the book is focused on Microsoft technology, ADFS (code name Geneva), FAM and WIF in particular. But I found the first 2 chapters very informative and well written.
E.g. interesting to have confirmation that applications need to keep maintaining fine grained (data level) authorizations themselves.
Also intersting to read about the challenge of home realm discovery: how to know to what Identity provider an external user should be redirected to.
One of the main challenges in my opionion with federated identity is the transformation of tokens/claims. Unless there is further standardization (profiles), the integration with each external business partners will require token transformations. There seems to be a general tendency in WS-land not to bother too much with the actual business content of SOAP messages or SAML tokens.
The day when SAML tokens can be used in an interoperable manner to connect to back-end applications such as SAP or Oracle will be a great day. Looking forward to it.
Authored by: Guy
