ABAP Authentication via LDAP (AD)

It sounds like an easy question, but I haven't been able to find a straight answer. I'm hoping someone here can help me.

Can APAB users authenticate driectly from Active Directory? My WAS 6.40 ABAP servers are running on Solaris, and I simply want to be able to authenticate users in a way similar to the way I do for EP. Can this be done?