Hi Rodrogo,
Basically what governs a tunnel-group is the group-policy associated with it.
If we already have ldap authentciation server setup on the ASA, we can configure:
1. AD to set the group-policy value to be in authorization-packet to the ASa
(Ex: User Properties > Organization > "Department")
2. Configure ASA so that it can read the value sent by the AD and place the user in that particular group-policy.
(configure ldap attribute-map and associate it with ldap server-group)
You have other options like, tunnel-group-lock.
Link:
http://www.cisco.com/en/US/docs/security/asa/asa82/configuration/guide/ref_extserver.html#wp1661573
Also you may explore DAP:
https://supportforums.cisco.com/docs/DOC-1369
HTH
Regards,
Praveen