Windows Identity Foundation integrates with WCF at the host level (ServiceHost) and then various WIF extensibility points are invoked at different stages of WCF message processing pipeline. This post show how WIF can be integrated with Workflow Services to enable common security scenarios. Additional rich security scenarios can also be enabled by using activities which're currently part of WF Security Pack project.
Now, check the picture below, it's worth 10^3 words….
….if you want to get deep-dive into check "Programming Windows Identity Foundation (Dev - Pro)" book available on Amazon.