Symfony3凭据无效，UsernameNotFoundException（代码：0）：用户名\＆＃34; \＆＃34;不存在

Question

登录教程：http://symfony.com/doc/current/security/form_login_setup.html

我在尝试登录时遇到错误：凭据无效。

这里有dev.log：

[2017-01-16 22:57:51] request.INFO: Matched route "login". {"route":"login","route_parameters":{"_controller":"AppBundle\\Controller\\SecurityController::loginAction","_route":"login"},"request_uri":"http://localhost:8000/login","method":"GET"} []
[2017-01-16 22:57:51] security.INFO: Populated the TokenStorage with an anonymous Token. [] [][2017-01-16 23:00:46] request.INFO: Matched route "login". {"route":"login","route_parameters":{"_controller":"AppBundle\\Controller\\SecurityController::loginAction","_route":"login"},"request_uri":"http://localhost:8000/login","method":"POST"} []
[2017-01-16 23:00:46] security.INFO: Authentication request failed. {"exception":"[object] (Symfony\\Component\\Security\\Core\\Exception\\BadCredentialsException(code: 0): Bad credentials. at /Users/mac/symfony-project/vendor/symfony/symfony/src/Symfony/Component/Security/Core/Authentication/Provider/UserAuthenticationProvider.php:73, Symfony\\Component\\Security\\Core\\Exception\\UsernameNotFoundException(code: 0): Username \"admin\" does not exist. at /Users/mac/symfony-project/vendor/symfony/symfony/src/Symfony/Component/Security/Core/User/InMemoryUserProvider.php:109)"} []

转储（$ authenticationUtils-＆GT; getLastAuthenticationError（））：

SecurityController.php on line 28:
BadCredentialsException {#100 ▼
  -token: UsernamePasswordToken {#99 ▼
    -credentials: "abcdef"
    -providerKey: "main"
    -user: "admin"
    -roles: []
    -authenticated: false
    -attributes: []
  }
  #message: "Bad credentials."
  #code: 0
  #file:     "../vendor/symfony/symfony/src/Symfony/Component/Security/Core/Authentication/Provider/UserAuthentication ▶"
  #line: 73

Security.yml

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

  providers:
      in_memory:
          memory: ~
      user_provider:
          entity:
              class: AppBundle\Entity\User
              property: username

  firewalls:
      main:
          anonymous: ~
          form_login:
              login_path: login
              check_path: login

SecurityController：

/**
 * @Route("/login", name="login")
 */
public function loginAction(Request $request)
{
    $form = $this->createForm(LoginType::class);

    $authenticationUtils = $this->get('security.authentication_utils');

    $a = 1;
    $a = 0;

    if ($a == 1)
        $error = $authenticationUtils->getLastAuthenticationError();
    else
        die(dump($authenticationUtils->getLastAuthenticationError()));

    $lastUsername = $authenticationUtils->getLastUsername();

    return $this->render('security/login.html.twig', array(
        'form' => $form->createView(),
        'last_username' => $lastUsername,
        'error' => $error,
    ));
}

登录表单：

<form action="{{ path('login') }}" method="post">
            <label for="username">Username:</label>
            <input type="text" id="username" name="_username" />

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

            <button type="submit">login</button>
        </form>

用户实体：

<?php

namespace AppBundle\Entity;

use Doctrine\ORM\Mapping as ORM;
use Symfony\Component\Security\Core\User\UserInterface;
use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity;
use Symfony\Component\Validator\Constraints as Assert;

/**
 * User
 *
 * @ORM\Table(name="user")
 * @ORM\Entity(repositoryClass="AppBundle\Repository\UserRepository")
 * @UniqueEntity(fields="username", message="Username already taken")
 */
class User implements UserInterface
{
    /**
     * @var int
     *
     * @ORM\Column(name="id", type="integer")
     * @ORM\Id
     * @ORM\GeneratedValue(strategy="AUTO")
     */
    private $id;

    /**
     * @var string
     * @Assert\NotBlank()
     * @ORM\Column(name="username", type="string", length=255, unique=true)
     */
    private $username;

    /**
     * @var string
     *
     * @ORM\Column(name="password", type="string", length=255)
     */
    private $password;

    /**
     * @var \DateTime
     *
     * @ORM\Column(name="created_at", type="datetime")
     */
    private $createdAt;

    /**
     * @Assert\NotBlank()
     * @Assert\Length(max=255)
     */
    private $plainPassword;

    public function __construct()
    {
        $this->createdAt = new \DateTime();
    }

    /**
     * Get id
     *
     * @return int
     */
    public function getId()
    {
        return $this->id;
    }

    /**
     * Set username
     *
     * @param string $username
     *
     * @return User
     */
    public function setUsername($username)
    {
        $this->username = $username;

        return $this;
    }

    /**
     * Get username
     *
     * @return string
     */
    public function getUsername()
    {
        return $this->username;
    }

    /**
     * Set password
     *
     * @param string $password
     *
     * @return User
     */
    public function setPassword($password)
    {
        $this->password = $password;

        return $this;
    }

    /**
     * Get password
     *
     * @return string
     */
    public function getPassword()
    {
        return $this->password;
    }

    /**
     * Set createdAt
     *
     * @param \DateTime $createdAt
     *
     * @return User
     */
    public function setCreatedAt($createdAt)
    {
        $this->createdAt = $createdAt;

        return $this;
    }

    /**
     * Get createdAt
     *
     * @return \DateTime
     */
    public function getCreatedAt()
    {
        return $this->createdAt;
    }

    /**
     * Get plain password
     *
     * @return string
     */
    public function getPlainPassword()
    {
        return $this->plainPassword;
    }

    /**
     * Set plain password
     *
     * @param string $password
     *
     * @return Users
     */
    public function setPlainPassword($password)
    {
        $this->plainPassword = $password;

        return $this;
    }

    public function getRoles()
    {
        return array('ROLE_USER');
    }

    public function eraseCredentials()
    {
    }

    public function getSalt()
    {
    }
}

哪里可能是问题？