Vittorio Bertocci has a nice high-level walkthrough of performing federation in a web service using the Geneva framework. Federation is a popular way of solving the trust problem when there are many different authorities of trust that an application has to deal with.
- ASP.NET, Geneva Framework & FedUtil.exe
- Using Geneva Server for adding a Relying Party relationship to the Identity Provider
For those interested in a more technical look, Dominick Baier has a separate pair of articles on how Geneva is integrated into WCF and ASP.NET.