authenticating to an Windows AD

Folks, I have freeradius running on a fedora linux box. I want to use it for authentication from an Apache web server using the radius interface. That part is working, and I'm able to authenticate web users only if they have a local account on the freeradius server. I want freeradius to authenticate against a Windows Active Directory. I installed Samba and am running Winbind, and wbinfo/ntlm_auth both are able to authenticate from the command line assuming I give it a valid username and password. What module in freeradius do I use to authenticate through Winbind? Could someone point me in the right direction please. -Mike