How to configure SSH to authenticate via OpenLDAP

Hi all,

I'm now working on a project of centralizing user authentication using
Active Directory and OpenLDAP. I've succeeded in configuring AD and OpenLDAP
as the authenticating server and users can login with console successfully.
However, when it comes to ssh, it failed to login. I use the 'ssh -v -v -v'
to see the details and I found no ldap connection had made by sshd to
authenticate users stored in the LDAP server. Can anyone give me some hints
on it? Thanks in advance.