private function getRemoteUser($serverKey) {
    if (!isset($this->users[$serverKey])) {
      $config = ObjectFactory::getInstance('configuration');
      $remoteUser = $config->getValue($serverKey, 'remoteuser');
      if (is_array($remoteUser) && sizeof($remoteUser) == 2) {
        $this->users[$serverKey] = [
          'login' => $remoteUser[0],
          'password' => $remoteUser[1]
        ];
      }
      else {
        throw new IllegialConfigurationException(
                "Remote user definition of '".$serverKey.
                "' must be an array of login and password."
        );
      }
    }
    return $this->users[$serverKey];
  }