写一个thinkphp登录代码

<?php
namespace app\index\controller;

use think\Controller;
use app\index\model\User;

class Login extends Controller
{
public function index()
{
return $this->fetch();
}

public function login()
{
$username = input('post.username');
$password = input('post.password');

$user = User::where('username', $username)->find();
if (!$user) {
$this->error('用户名不存在！');
}

if ($user->password != md5($password)) {
$this->error('密码错误！');
}

session('user_id', $user->id);
session('username', $user->username);

$this->success('登录成功！', url('index/index'));
}

public function logout()
{
session(null);
$this->success('退出成功！', url('login/index'));
}
}