/**
  * Delete the sid from LDAP.
  */
 public function deleteSid()
 {
     $attributes[$this->getSidAttribute()] = array();
     if (!$this->server->modify($this->dn, $attributes, 'delete')) {
         throw new Exception('Unable to delete session id from LDAP.');
     }
     $this->hashedSid = NULL;
 }