mikrotik+RADIUS

RADIUS, short for Remote Authentication Dial-In User Service, is a remote server that provides authentication and accounting facilities to various network apliances. RADIUS authentication and accounting gives the ISP or network administrator ability to manage PPP user access and accounting from one server throughout a large network. The MikroTik RouterOS has a RADIUS client which can authenticate for HotSpot, PPP, PPPoE, PPTP, L2TP and ISDN connections.

The RADIUS server database is consulted only if no matching user acces record is found in router's local database.

Увы, только клиент. Но хорошо интегрируется с LDAP

http://wiki.mikrotik.com/wiki/Manual:RADIUS_Client
http://wiki.mikrotik.com/wiki/How_to_setup_up_RADIUS_for_use_with_MikroTik_-_By_Ramona