private function rename(PFUser $old_user, PFUser $new_user)
 {
     $new_dn = $this->getUserDN($new_user);
     $old_dn = $this->getUserDN($old_user);
     if ($new_dn != $old_dn) {
         $this->ldap->renameUser($old_dn, $this->getUserRDN($new_user));
         $this->updateUserLdapId($new_user);
     }
 }