CAS includes a number of security features that are designed to limit the damage caused by a security breach in a client application. Specifically, CAS scopes the CAS TGT cookie, which holds the Single Sign On credentials to only be delivered to the CAS server itself. CAS client applications therefore do not have access to any central credential which could be used to gain access to other CAS protected services. CAS clients instead perform a service ticket validation, which results in CAS providing and authenticated user id to the requesting client application. It is then up to the client application to set up a secure session and handle expiration and renewal of that session.
Therefore, a user's CAS single sign on session consists of a single TGT scoped to the CAS server and numerous sessions scoped to the client application servers. This presents a problem when attempting to log the user out of all services during the CAS logout process.