Wikipedia
Terminal Access Controller Access-Control System (TACACS, ) refers to a family of related protocols handling remote authentication and related services for networked access control through a centralized server. The original TACACS protocol, which dates back to 1984, was used for communicating with an authentication server, common in older UNIX networks; it spawned related protocols:
Extended TACACS (XTACACS) is a proprietary extension to TACACS introduced by Cisco Systems in 1990 without backwards compatibility to the original protocol. …
TACACS - Wikipedia, the free encyclopedia