[CentOS] HTTP authentication/authorisation for Apache & AD.

I am looking into the best way to integrate active directory user
authentication and authorisation in to Apache.

So far I have a working LDAP solution that requires the
username/password to be entered and a Kerberos setup that is transparent
to the user but with no authorisation.

Searching the net seems to only find commercial offerings which offer
true password less integration between AD & Apache.

Is there a open source or inexpensive way to achieve what I want?

Thanks

Dean