code: protected function getValidHostGroups($requestHost)
      {
          $validGroups = array();
  
          foreach ($this->httpHostGroups as $group => $hostnames) {
              if (in_array($requestHost, $hostnames)) {
                  $validGroups[] = $group;
              }
          }
  
          return $validGroups;
      }
docs: @param string $requestHost
  
  @return array