/**
  * @param  Credentials $credentials
  * @return void
  */
 protected function _updateCredentialsLastUsage(Credentials $credentials)
 {
     $sm = $this->getServiceLocator();
     /** @var \Doctrine\ORM\EntityManager $em */
     $em = $sm->get('em');
     $credentials->setLastUsedAt(new \DateTime());
     $em->persist($credentials);
     $em->flush($credentials);
 }