So, I'm creating an ASP.NET MVC application to be hosted in Azure. It's currently authenticating users via Azure ACS which delegates to a number of IdPs of clients for the application.
The application now needs to call into a WCF service to display some information, but the services need to be secured. I had originally though to use the WS-Trust protocol and pass the identity through the application using an "ActAs" token, however Azure ACS 2.0 will not issue tokens of this type.
How can I obtain an access token for the services based on the user's current identity? I can go back to the ACS for additional tokens, but the system mustn't prompt for the user to provide credentials each time.