namespace App\Http\Controllers\Auth;
......
use Illuminate\Http\Request; // 增加该行

class AuthController extends Controller
{
    protected $username = 'login';

    ....

    protected function getCredentials(Request $request)
    {
        $login = $request->get('login');
        $field = filter_var($login, FILTER_VALIDATE_EMAIL) ? 'email' : 'name';

        return [
            $field => $login,
            'password' => $request->get('password'),
        ];
    }
}

namespace App\Http\Controllers\Auth;
......
use Illuminate\Http\Request; // 增加该行

class AuthController extends Controller
{

    // 修改这里
    use AuthenticatesAndRegistersUsers, ThrottlesLogins {
        AuthenticatesAndRegistersUsers::postLogin as laravelPostLogin;
    }

    ......

    // 增加方法
    public function postLogin(Request $request)
    {
        $field = filter_var($request->input('login'), FILTER_VALIDATE_EMAIL) ? 'email' : 'name';
        $request->merge([$field => $request->input('login')]);
        $this->username = $field;

        return self::laravelPostLogin($request);
    }
}

public function rules()
{
    return [
       'login' => 'required',
       'password' => 'required'
    ];
}

public function login(LoginRequest $request)
{
    $field = filter_var($request->input('login'), FILTER_VALIDATE_EMAIL) ? 'email' : 'username';
    $request->merge([$field => $request->input('login')]);

    if ($this->auth->attempt($request->only($field, 'password')))
    {
        return redirect('/');
    }

    return redirect('/login')->withErrors([
        'error' => 'These credentials do not match our records.',
    ]);
}