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?

Role-Based Access Control (RBAC) is an authorization model that grants or restricts system access to users based on their assigned roles, rather than facilitating a single authentication for multiple distinct systems.

Discretionary Access Control (DAC) is an authorization model where the resource owner determines who can access the resource and what permissions they have, which is different from a unified authentication mechanism across multiple systems.

Single sign-on (SSO) is an authentication scheme that allows a user to log in with a single set of credentials and access multiple applications or systems that trust the central authentication server (CAS). This streamlines the user experience and improves security by reducing the number of passwords users need to manage.

Windows authentication is a specific implementation of authentication used within Microsoft environments (e.g., Active Directory), which can support SSO, but it is not the general conceptual mechanism of single sign-on itself for disparate systems.