Symfony4 Login Form Type

login.html.twig

{% extends 'base.html.twig' %}

{% block body %}
  <form action="{{ path('login') }}" method="post">
    {{ form_widget(form) }}

    {# Note: ensure the submit name does not conflict with the form's name or it may clobber field data #}
    <input type="submit" name="login" />
  </form>
{% endblock %}

LoginController.php

<?php

use LoginType;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Sensio\Bundle\FrameworkExtraBundle\Configuration\Template;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;

final class LoginController extends Controller
{
    /**
     * @Route("/login", name="login")
     * @Template(template="login.html.twig")
     */
    public function loginAction()
    {
        $form = $this->createForm(LoginType::class);

        return [
            'login_form' => $form->createView(),
        ];
    }
}

LoginType.php

<?php

use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\PasswordType;
use Symfony\Component\Form\Extension\Core\Type\TextType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Form\FormError;
use Symfony\Component\Form\FormEvent;
use Symfony\Component\Form\FormEvents;
use Symfony\Component\OptionsResolver\OptionsResolver;
use Symfony\Component\Security\Http\Authentication\AuthenticationUtils;

final class LoginType extends AbstractType
{
    /**
     * @var AuthenticationUtils
     */
    private $authenticationUtils;

    public function __construct(AuthenticationUtils $authenticationUtils)
    {
        $this->authenticationUtils = $authenticationUtils;
    }

    /**
     * {@inheritdoc}
     */
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            ->add('_username', TextType::class)
            ->add('_password', PasswordType::class)
            ->add('_target_path', 'Symfony\Component\Form\Extension\Core\Type\HiddenType')
        ;

        $authUtils = $this->authenticationUtils;

        $builder->addEventListener(FormEvents::PRE_SET_DATA, function (FormEvent $event) use ($authUtils) {
            // get the login error if there is one
            $error = $authUtils->getLastAuthenticationError();

            if ($error) {
                $event->getForm()->addError(new FormError($error->getMessage()));
            }

            $event->setData(array_replace((array) $event->getData(), array(
                '_username' => $authUtils->getLastUsername(),
            )));
        });
    }

    /**
     * {@inheritdoc}
     */
    public function configureOptions(OptionsResolver $resolver)
    {
        /* Note: the form's csrf_token_id must correspond to that for the form login
         * listener in order for the CSRF token to validate successfully.
         */

        $resolver->setDefaults(array(
            'csrf_token_id' => 'authenticate',
        ));
    }

    public function getBlockPrefix()
    {
        return '';
    }
}