SymfonyUserProvider.php

<?php

namespace AppBundle\Security\User;

use AppBundle\Entity\User;
use Doctrine\ORM\EntityManagerInterface;
use Symfony\Component\Security\Core\User\UserInterface;
use Symfony\Component\Security\Core\User\UserProviderInterface;
use Symfony\Component\Security\Core\Exception\UsernameNotFoundException;

class DefaultProvider implements UserProviderInterface
{
    protected $em;

    public function __construct(EntityManagerInterface $em)
    {
        $this->em = $em;
    }

    public function loadUserByUsername($username)
    {
        $repository = $this->em->getRepository(User::class);

        if (!$entity = $repository->find($username)) {
            throw new UsernameNotFoundException(
                sprintf('Username "%s" does not exist.', $username)
            );
        }

        return $entity;
    }

    public function refreshUser(UserInterface $user)
    {
        $class = get_class($user);

        if (!$this->supportsClass($class)) {
            throw new UnsupportedUserException(
                sprintf('Instances of "%s" are not supported.', $class)
            );
        }

        return $this->loadUserByUsername($user->getId());
    }

    public function supportsClass($class)
    {
        return ($class === User::class);
    }
}