The Central Authentication Service (CAS) is an Internet single sign-on protocol. It allows users to access multiple applications while providing their credentials (such as user ID 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. The name CAS also refers to a software package that implements this protocol.

Replicon works with SAML authentication (Security Assertion Markup Language), but not CAS.