I am configuring windows nt authentication on asa 5520 firewall for clientless web vpn. is there a way i can specify to only authentication from the specific AD group only using windows nt or other way?
It is possible using LDAP. You can define the base dn as the group you want to search in AD. You will have to change the :LDAP scope as single-level i.e.One level beneath the Base DN.
Here is a link which will help you in configuring the LDAP for Webvpn: