laravel中身份验证实现

laravel中检测用户是否登录，有以下的代码：
if ( !Auth::guest() )
        {
            return Redirect::to('/dashboard');
        }

那Auth::guest是如何调用的呢？
laravel用了Facade模式，相关门面类在laravel/framework/src/Illuminate/Support/Facades文件夹定义的，看下Auth类的定义：
class Auth extends Facade {

    /**
     * Get the registered name of the component.
     *
     * @return string
     */
    protected static function getFacadeAccessor() { return 'auth'; }

}

laravel框架中，Facade模式使用反射，相关方法其实调用app['auth']中的方法，app['auth']是什么时候创建的呢，
 AuthServiceProvider::register方法会注册：
$this->app->bindShared('auth', function($app)
        {
            // Once the authentication service has actually been requested by the developer
            // we will set a variable in the application indicating such. This helps us
            // know that we need to set any queued cookies in the after event later.
            $app['auth.loaded'] = true;

            return new AuthManager($app);
        });

那为什么最终会调到哪里呢，看下堆栈：

Illuminate\Support\Facades\Auth::guest()
Illuminate\Support\Facades\Facade::__callStatic
Illuminate\Auth\AuthManager->guest()
Illuminate\Support\Manager->__call

public function __call($method, $parameters)
    {
        return call_user_func_array(array($this->driver(), $method), $parameters);
    }

看下driver的代码，
public function driver($driver = null)
    {
        $driver = $driver ?: $this->getDefaultDriver();

        // If the given driver has not been created before, we will create the instances
        // here and cache it so we can return it next time very quickly. If there is
        // already a driver created by this name, we'll just return that instance.
        if ( ! isset($this->drivers[$driver]))
        {
            $this->drivers[$driver] = $this->createDriver($driver);
        }

        return $this->drivers[$driver];
    }

没有会调用getDefaultDrive方法
/**
     * Get the default authentication driver name.
     *
     * @return string
     */
    public function getDefaultDriver()
    {
        return $this->app['config']['auth.driver'];
    }

最终调用的是配置文件中配置的driver，如果配的是
'driver' => 'eloquent'

则调用的是
public function createEloquentDriver()
    {
        $provider = $this->createEloquentProvider();

        return new Guard($provider, $this->app['session.store']);
    }

所以Auth::guest最终调用的是Guard::guest方法
这里的逻辑先从session中取用户信息，奇怪的是session里只保存的是用户ID，然后拿这个ID来从数据库中取用户信息

public function user()
    {
        if ($this->loggedOut) return;

        // If we have already retrieved the user for the current request we can just
        // return it back immediately. We do not want to pull the user data every
        // request into the method because that would tremendously slow an app.
        if ( ! is_null($this->user))
        {
            return $this->user;
        }

        $id = $this->session->get($this->getName());

        // First we will try to load the user using the identifier in the session if
        // one exists. Otherwise we will check for a "remember me" cookie in this
        // request, and if one exists, attempt to retrieve the user using that.
        $user = null;

        if ( ! is_null($id))
        {
            //provider为EloquentUserProvider
          $user = $this->provider->retrieveByID($id);
        }

        // If the user is null, but we decrypt a "recaller" cookie we can attempt to
        // pull the user data on that cookie which serves as a remember cookie on
        // the application. Once we have a user we can return it to the caller.
        $recaller = $this->getRecaller();

        if (is_null($user) && ! is_null($recaller))
        {
            $user = $this->getUserByRecaller($recaller);
        }

        return $this->user = $user;
    }