I fixed the issue.
AuthLDAPBindDN "CN=service-account,OU=ProcessIDs,OU=Logical Secure,OU=
+Core Directory Service,DC=DOMAIN,DC=com"
I found that at AuthLDAPURL line we need to use the authenticated user's DN details + the filter information and at AuthLDAPBindDN line we need to put the service account's dn details.
All is well. I learn by answering your questions...