FOS\UserBundle\Model\UserInterface::setUsernameCanonical PHP Method

    function setUsernameCanonical($usernameCanonical);

 /**
  * {@inheritdoc}
  */
 public function updateCanonicalFields(UserInterface $user)
 {
     $user->setUsernameCanonical(strtolower($user->getUsername()));
     $user->setEmailCanonical(strtolower($user->getEmail()));
 }