>> I'm using an OpenLDAP with the domain ud.example.org.
Say.. your user is in one tree named 'ou=people,o=example,o=org' in that OpenLDAP.
you need to import that specific tree, this will be used as 'baseDN' in Gluu Server.
And you need to make sure that you have some user who can 'read' that tree. That user's username will be 'bindDN' ( full DN of that user ) and password will be 'bindDN password'.