There is no built-in Active Directory authentication scheme. There is a built-in LDAP scheme which, if you provide the right DN, will work in most environments where you have AD. Search this forum for Active Directory.
That correct I am using the LDAP scheme, and providing it with the appropriate DN string. The only problem is that it allways says authentication failed, without giving any error messages. So I tried with some success to test the LDAP packages provided by oracle.
I am able to authenticate using dbms_ldap, but that only works when I provide NULL for a password.