This page describes how to integrate Seam's Identity component (a.k.a - Seam Security) with a CAS Server. My approach is based on the Yale CAS Client distribution. See also here and here
Configure your web.xml as directed in the Yale CAS Client distribution docs to use CAS for login and logout.
2. Write a Seam-Identity authenticator class / component:
Configure Seam's pages.xml file in your web app to use your authenticator.