authenticator.php

<?php

use Symfony\Component\HttpFoundation\Session\SessionInterface;

class AppDefaultAuthenticator extends AbstractGuardAuthenticator implements AuthenticatorInterface
{
  ...
  private $session;
  ...
  public function __construct(SessionInterface $session) {
    $this->session = $session;
  }
  ...
  public function getCredentials(Request $request)
  {
    $this->session->set(
      Security::LAST_USERNAME,
    );
  }
  ...
}