Which access control mechanism allows for multiple systems to use a central authentication server (CAS) that permits users to authenticate once and gain access to multiple systems?

SSO with a Central Authentication Server (CAS) authenticates the user a single time and issues a session token or ticket (such as a Kerberos TGT or SAML assertion) that is accepted by all participating systems, eliminating repeated logins while centralizing authentication management.

Windows Authentication refers to NTLM or Kerberos protocols specific to Microsoft environments and does not describe a vendor-neutral CAS architecture that federates authentication across heterogeneous systems.

RBAC is an authorization model that assigns permissions based on user roles, not an authentication mechanism; it does not provide centralized login or eliminate the need for separate credentials per system.

DAC is an authorization model where resource owners control access permissions; it addresses who can access resources, not how users authenticate or how login sessions are federated.