working with LDAP authorization hook
I've been down this route a few times (looking at using LDAP integration module) each time I ended up writing my own LDAP integration.  Everyone implements differently, I just take the pieces I like from the LDAP module out there (6 or 7) and use your own code to do it.  As a general rule, anytime the rubber hits the road with integrating Drupal with user authentication / authorization systems in an organization I brute force them together via a custom / forked module.  You'll always know your own auth system's specific needs, D.O. will not :)