Central Authentication Service (CAS)

Central Authentication Service (CAS) is an open-source single sign-on (SSO) protocol and reference implementation originally developed by Yale University. It provides web-based authentication, session management, and ticket-granting mechanisms for applications within an organization or across domains. The project is now maintained by Apereo Foundation as the official Apereo CAS Server.

Key Capabilities

• Open standard and open-source implementation: Freely available under the Apereo Foundation; widely adopted by universities and enterprises seeking self-hosted SSO.

• Centralized authentication: Users authenticate once to the CAS server and obtain tickets that grant access to multiple services without re-entering credentials.

• Protocol support: Native CAS protocol (ticket-based), with extensions for SAML 2.0, OpenID Connect, and OAuth 2.0 for federated and modern web applications.

• Directory and identity integration: Supports LDAP, Active Directory, JDBC, and custom identity stores for credential validation and attribute release.

Limitations

• Self-managed infrastructure: Requires hosting, scaling, and maintenance by the organization; no vendor-managed SaaS offering.

• Complex configuration: Multi-protocol and attribute-release configuration can require significant expertise in Spring and identity standards.

• Limited built-in lifecycle management: CAS focuses on authentication; provisioning, deprovisioning, and governance rely on external systems (e.g., SCIM-capable IAM).

• UI/UX customization effort: Default login UI and flows often require manual branding and development for production CIAM experiences.

• Protocol variance: The proprietary CAS protocol differs from OAuth/OIDC; interoperability with non-CAS apps requires dedicated clients or extensions.