[FIXED] How to manually authenticate user after Registration with the new Symfony 5 Authenticator?

Issue

Symfony 5 has changed its guard authentication method to a new Passport based one, using the new security config: enable_authenticator_manager: true;

I would like to know how to authenticate a user in the Registration form method in my controller, after the user is persisted by the ORM (Doctrine);

I have succeeded in authenticating the user using the login form, but I still do not know how to manually do this.

Solution

As per Cerad's comment, here is the full answer.

Below is only the part of the code related to the question & answer. These are not the full files.

Also, this is only for Symfony ^5.2 that is not using guard to authenticate the user.

/* config/packages/security.yaml */

security:
    enable_authenticator_manager: true
    firewalls:
        main:
            custom_authenticators:
                - App\Security\SecurityAuthenticator

/* src/Security/SecurityAuthenticator.php */

use Symfony\Component\Security\Http\Authenticator\AbstractLoginFormAuthenticator;

/* automatically generated with the make:auth command,
     the important part is to undestand that this is not a Guard implement 
     for the Authenticator class */
class SecurityAuthenticator extends AbstractLoginFormAuthenticator
{
  
}

/* src/Controller/RegistrationController.php */

use App\Entity\User;
use App\Form\RegistrationFormType;
use App\Security\SecurityAuthenticator;

use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Routing\Annotation\Route;
use Symfony\Component\Security\Core\Encoder\UserPasswordEncoderInterface;
use Symfony\Component\Security\Http\Authentication\UserAuthenticatorInterface;

class RegistrationController extends AbstractController
{

    /**
     * @Route("/register", name="app_register")
     */
    public function register(
        Request $request, 
        UserPasswordEncoderInterface $passwordEncoder, 
        UserAuthenticatorInterface $authenticator, 
        SecurityAuthenticator $formAuthenticator): Response
    {
      /* Automatically generated by make:registration-form, but some changes are
         needed, like the auto-wiring of the UserAuthenticatorInterface and 
         SecurityAuthenticator */
        $user = new User();
        $form = $this->createForm(RegistrationFormType::class, $user);
        $form->handleRequest($request);

        if ($form->isSubmitted() && $form->isValid()) {
            // encode the plain password
            $user->setPassword($passwordEncoder->encodePassword($user, $form->get('password')->getData()));

            $entityManager = $this->getDoctrine()->getManager();
            $entityManager->persist($user);
            $entityManager->flush();

            // substitute the previous line (redirect response) with this one.
            return $authenticator->authenticateUser(
                $user, 
                $formAuthenticator, 
                $request); 
        }

        return $this->render('registration/register.html.twig', [
            'registrationForm' => $form->createView(),
        ]);
    }
}

Answered By - Rodolfo Rangel