"... an engineer who is not only competent at the analytics and technologies of engineering, but can bring value to clients, team well, design well, foster adoptions of new technologies, position for innovations, cope with accelerating change and mentor other engineers" -- CACM 2014/12
Up till now, I thought that TACACS use was limited to authentication/authorization of logins and commands on Cisco devices. There is an article at Freemode.net regarding TACACS + Linux for authentication.