public static function getInstance()
 {
     if (!isset(FederatedConfiguration::$instance)) {
         FederatedConfiguration::$instance = new FederatedConfiguration();
     }
     return FederatedConfiguration::$instance;
 }
 protected function getThumprints()
 {
     if ($this->thumbprint !== null) {
         return array($this->thumbprint);
     } else {
         return array(FederatedConfiguration::getInstance()->getThumbprint());
     }
 }