ldap newbie here, tia for assistance

want to use one repository (like AD) for authentication yet reference another repository (Sun One) for authorization to applications <since AD doesn't support multiple groups/roles/schema changes well>.

example
So for application A, want to have the userID/pw authentication use AD, but for authorization to appl A, B, C, want to query SunOne to obtain that info and place into HTTP header for use by the applicaiton(s).
can someone assist on how to do this?