Пользовательский поставщик Symfony3 не работает

Я пытался реализовать все в соответствии с документацией Symfony, но, похоже, аутентификация не работает вообще. Посмотрите, что именно я сделал:

security.yml

security:
encoders:
AppBundle\Entity\StUser:
algorithm: bcrypt
cost: 12

providers:
our_db_provider:
entity:
class: AppBundle:Entity:StUser

firewalls:
user_secured_area:
pattern:   ^/([a-z]{2})/account
provider: our_db_provider
form_login:
login_path: login
check_path: login_check
csrf_token_generator: security.csrf.token_manager
default:
anonymous: ~
http_basic: ~

Объект StUser.php

namespace AppBundle\Entity;

class StUser implements UserInterface
{
private $id;
private $firstName;
private $lastName;
private $password;
private $username;
private $isAdmin = '0';
private $confirmed;
private $created = 'CURRENT_TIMESTAMP';
private $status = '1';

public function getId()
{
return $this->id;
}

public function setFirstName($firstName)
{
$this->firstName = $firstName;

return $this;
}

public function getFirstName()
{
return $this->firstName;
}

public function setLastName($lastName)
{
$this->lastName = $lastName;

return $this;
}

public function getLastName()
{
return $this->lastName;
}

public function setPassword($password)
{
$this->password = $password;

return $this;
}

public function getPassword()
{
return $this->password;
}

public function setUsername($username)
{
$this->username = $username;

return $this;
}

public function getUsername()
{
return $this->username;
}

public function setIsAdmin($isAdmin)
{
$this->isAdmin = $isAdmin;

return $this;
}

public function getIsAdmin()
{
return $this->isAdmin;
}

public function setConfirmed($confirmed)
{
$this->confirmed = $confirmed;

return $this;
}

public function getConfirmed()
{
return $this->confirmed;
}

public function setCreated($created)
{
$this->created = $created;

return $this;
}

public function getCreated()
{
return $this->created;
}

public function setStatus($status)
{
$this->status = $status;

return $this;
}

public function getStatus()
{
return $this->status;
}

/* ==== Additional =================================================== */
public function __construct($username, $password, $salt, array $roles)
{
$this->username = $username;
$this->password = $password;
/* $this->salt = $salt; */
/* $this->roles = $roles; */
}

public function getRoles()
{
return null;
}

public function getSalt()
{
return null;
}

public function eraseCredentials()
{

}
}

Репозиторий UserRepository.php:

namespace AppBundle\Repository;

use Symfony\Bridge\Doctrine\Security\User\UserLoaderInterface;
use Doctrine\ORM\EntityRepository;

class UserRepository extends EntityRepository implements UserLoaderInterface
{
public function loadUserByUsername($username)
{
return $this->createQueryBuilder('u')
->where('u.username = :username OR u.email = :email')
->setParameter('username', $username)
->setParameter('email', $username)
->getQuery()
->getOneOrNullResult();
}
}

AccountController.php

namespace AccountBundle\Controller;

use Sensio\Bundle\FrameworkExtraBundle\Configuration\Route;
use Symfony\Bundle\FrameworkBundle\Controller\Controller;
use Symfony\Component\HttpFoundation\Request;

class AccountController extends Controller
{
/**
* @Route("{_lang}/login", name="login", requirements={"_lang": "pl"})
*/
public function loginAction(Request $request, $_lang = '')
{
$helper = $this->get('security.authentication_utils');
$error = $helper->getLastAuthenticationError();

var_dump( $error );

return $this->render('account/login.html.twig', array(
'projects' => "",
'lang' => "pl",
'allLangs' => "",
'mainLang' => "",
'meta_title' => "test",
'meta_description' => "",
'meta_keywords' => "",
'meta_robots' => "",
'image_src' => "",
'social_title' => "",
'social_description' => "",
'social_url' => "",
'aaaa' => $helper,

/* 'last_username' => $lastUsername,
'error'         => $error, */
));
}
}

login.html.twig view

{% block body %}
<form action="{{ path('login', {'_lang': lang}) }}" method="post">
<label for="username">Username:</label>
<input type="text" id="username" name="_username" value="" />

<label for="password">Password:</label>
<input type="password" id="password" name="_password" />

<input type="hidden" name="_csrf_token" value="{{ csrf_token('authenticate') }}">

<button type="submit">login</button>
</form>
{% endblock %}

И ничего не происходит, $ helper и $ error пустые / нулевые, я ничего не могу найти в логах. Что я пропустил. Заранее спасибо.