private function _getKey($id)
 {
     $url = E3_PROV_URL_KEY . "/" . rawurlencode($id);
     $reply = $this->restClient->makeCall($url, "GET");
     $xml = simplexml_load_string($reply->getPayload());
     if ($reply->getHTTPCode() === "200") {
         $auth = SSLKey::fromXML($xml->key);
         return $auth;
     } else {
         throw new Exception(!empty($xml->error) ? $xml->error->errorText : UNDEFINED_ERROR_TEXT);
     }
 }