/**
  * Helper function that returns the event listener.
  *
  * @param Acquia\Search\AcquiaSearchClient $solr
  *
  * @return \Acquia\Search\AcquiaSearchAuthPlugin
  *
  * @throws \UnexpectedValueException
  */
 public function getRegisteredAuthPlugin(AcquiaSearchClient $solr)
 {
     $listeners = $solr->getEventDispatcher()->getListeners('request.before_send');
     foreach ($listeners as $listener) {
         if (isset($listener[0]) && $listener[0] instanceof AcquiaSearchAuthPlugin) {
             return $listener[0];
         }
     }
     throw new \UnexpectedValueException('Expecting subscriber Acquia\\Search\\AcquiaSearchAuthPlugin to be registered');
 }