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 and XTACACS both allow a remote access server to communicate with an authentication server in order to determine if the user has access to the network
TACACS - Wikipedia, the free encyclopedia