It is quite incredible what FreeRadius can do. At a customer site I've got a server which is doing authentication and authorization (as well as accounting of course) for a number of different NAS, each servicing distinct groups of people. Examples are VPN users, regular dial-up, Wireless with 802.1x and also administrative ssh logins to Cisco routers. Oh, and the best part? All managed by an OpenLDAP directory as a backend.