The Windows Azure Access Control Service (ACS) enables federated authentication, but all the examples I've seen has been of passive federation (browser-based applications authenticating via a sequence of HTTP redirects and scripted HTTP posts).
Does the ACS support active federation?
In other words: assume that we have a rich client like a WPF or Silverlight application that accesses a web service. Is it possible to use the ACS as an STS in this scenario?
Yes, this is possible. If you check the examples in the excellent Identity Training Kit or at acs.codeplex.com, you are interested in looking at the ones for 'web services' as opposed to web sites.
Here are a couple of such examples:
http://msdn.microsoft.com/en-us/IdentityTrainingCourse_WebServicesAndIdentityLab2010
http://acs.codeplex.com/wikipage?title=WCF%20Federated%20Authentication&referringTitle=Samples
来源：https://stackoverflow.com/questions/5818080/is-it-possible-to-use-active-federation-with-the-azure-access-control-service