I just searched this yesterday looking for the same answer. There is almost no documentation on this specific setup but there is a Cisco document "Kerberos Authentication and LDAP Authorization Server Groups".
Link Only in our case SDI is for authentication and ldap for authorization.
Simply setup an aaa-server group for the rsa like you normally would for authentication. Then setup an aaa-server group for ldap the same way as if you are using it for authentication and add the appropriate ldap attribute maps to associate the ldap memberOf (AD groups) with group policy.
Then on your tunnel group select the rsa aaa-server group for authentication. Go to the authorization section and select the ldap aaa-server group for authorization.
That's it.