class Authenticator extends AbstractGuardAuthenticator
{
    private $encoderFactory;
    private $userRepository;
    private $tokenStorage;
    private $router;

public function __construct(EncoderFactoryInterface $encoderFactory, UserRepositoryInterface $userRepository, TokenStorageInterface $tokenStorage, Router $router)
{
    $this->encoderFactory = $encoderFactory;
    $this->userRepository = $userRepository;
    $this->tokenStorage = $tokenStorage;
    $this->router = $router;
}

/**
 * Called on every request. Return whatever credentials you want,
 * or null to stop authentication.
 */
public function getCredentials(Request $request)
{
    $encoder = $this->encoderFactory->getEncoder(new User());
    $displayname = $request->request->get('_username');
    $password = $request->request->get('_password');

    $users = $this->userRepository->findByDisplayname($displayname);

    if ($users !== []) {
        foreach ($users as $user) {
            if ($encoder->isPasswordValid($user->getPassword(), $password, $user->getSalt())) {
                return ['username' => $user->getUsername(), 'password' => $user->getPassword()];
            }
        }
    } else {
        if ($this->tokenStorage->getToken() !== null) {
            $user = $this->tokenStorage->getToken()->getUser();

            return ['username' => $user->getUsername(), 'password' => $user->getPassword()];
        }
    }

    return null;
}

public function getUser($credentials, UserProviderInterface $userProvider)
{
    if ($credentials !== null) {
        return $userProvider->loadUserByUsername($credentials["username"]);
    }

    return null;
}

public function checkCredentials($credentials, UserInterface $user)
{
    if ($user !== null) {
        return true;
    } else {
        return false;
    }
}

public function onAuthenticationSuccess(Request $request, TokenInterface $token, $providerKey)
{
    return null;
}

public function onAuthenticationFailure(Request $request, AuthenticationException $exception)
{
    $exclusions = ['/login'];

    if (!in_array($request->getPathInfo(), $exclusions)) {
        $request->getSession()->set(Security::AUTHENTICATION_ERROR, $exception);
        throw $exception;
    }
}

/**
 * Called when authentication is needed, but it's not sent
 */
public function start(Request $request, AuthenticationException $authException = null)
{
    $data = array(
        // you might translate this message
        'message' => 'Authentication Required'
    );

    return new JsonResponse($data, Response::HTTP_UNAUTHORIZED);
}

public function supportsRememberMe()
{
    return false;
}
}

class CustomAuthListener extends UsernamePasswordFormAuthenticationListener
{
    private $csrfTokenManager;
    private $tokenStorage;

public function __construct(TokenStorageInterface $tokenStorage, AuthenticationManagerInterface $authenticationManager, SessionAuthenticationStrategyInterface $sessionStrategy, HttpUtils $httpUtils, $providerKey, AuthenticationSuccessHandlerInterface $successHandler, AuthenticationFailureHandlerInterface $failureHandler, array $options = array(), LoggerInterface $logger = null, EventDispatcherInterface $dispatcher = null, CsrfTokenManagerInterface $csrfTokenManager = null)
{
    parent::__construct($tokenStorage, $authenticationManager, $sessionStrategy, $httpUtils, $providerKey, $successHandler, $failureHandler, array_merge(array(
        'username_parameter' => '_username',
        'password_parameter' => '_password',
        'csrf_parameter' => '_csrf_token',
        'csrf_token_id' => 'authenticate',
        'post_only' => true,
    ), $options), $logger, $dispatcher);

    $this->csrfTokenManager = $csrfTokenManager;
    $this->tokenStorage = $tokenStorage;
}

/**
 * {@inheritdoc}
 */
protected function attemptAuthentication(Request $request)
{
    if ($user = $this->tokenStorage->getToken() !== null) {
        $user = $this->tokenStorage->getToken()->getUser();
        $username = $user->getUsername();

        if ($this->options['post_only']) {
            $password = ParameterBagUtils::getParameterBagValue($request->request, $this->options['password_parameter']);
        } else {
            $password = ParameterBagUtils::getRequestParameterValue($request, $this->options['password_parameter']);
        }

        if (strlen($username) > Security::MAX_USERNAME_LENGTH) {
            throw new BadCredentialsException('Invalid username.');
        }

        $request->getSession()->set(Security::LAST_USERNAME, $username);

        return $this->authenticationManager->authenticate(new UsernamePasswordToken($username, $password, $this->providerKey));
    } else {
        return null;
    }
}
}

<service id="security.authentication.listener.form" class="YourPathToCustomAuthListener" parent="security.authentication.listener.abstract" abstract="true" />