Central Authentication Service, a trusted system to authenticate a user. For Code Access Security (Microsoft .NET) use the [code-access-security] tag
The Central Authentication Service (CAS) is a single sign-on protocol for the web. Its purpose is to permit a user to access multiple applications while providing their credentials (such as userid and password) only once. It also allows web applications to authenticate users without gaining access to a user's security credentials, such as a password.