This administratively enables or disables using TACACS+ specifically for user authentication, verifying login credentials, on this device. This is distinct from the broader client-wide admin-state switch and from the separate authorization and accounting toggles, so an admin can, for instance, use TACACS for centralized authentication while leaving authorization decisions to a local policy, or vice versa, a common intentional configuration rather than an oversight. For example, a shop that wants centralized login credential checking via TACACS but prefers to manage command-authorization rules locally would enable this object while leaving the authorization admin state disabled.