I'm still unclear what needs to be passed into the headers or how this plug works. Maybe someone can let me know if I'm on the right track here.
The passthru plugin looks for the REMOTE_USER header, containing the name it'll use to search for in the ldap lookup. Such as the sAMAccountName value. If it finds them, it'll then look for a matching user name the osticket user db. If the user isn't found in osticket, it'll create them. Does this sound correct?