namespace App\Http\Controllers;
use Illuminate\Http\Request;
use Illuminate\Foundation\Auth\ThrottlesLogins;
class AuthController extends Controller
{
 use ThrottlesLogins;
 ......

public function login(Request $request)
{
 // Authenticate Inputs
 $request->validate([
 'username' => 'required', 
 'password' => 'required|min:6|max:18'
 ]);
 // If the class is using the ThrottlesLogins trait, we can automatically throttle
 // the login attempts for this application. We'll key this by the username and
 // the IP address of the client making these requests into this application.
 if (method_exists($this, 'hasTooManyLoginAttempts') &&
 $this->hasTooManyLoginAttempts($request)) {
 $this->fireLockoutEvent($request);
 return $this->sendLockoutResponse($request);
 }
 
 .......

if( Auth::attempt(['username' => $username, 'password' => $password]) ){
 // Redirect to appropriate dashboard 
}
else {
 // If the login attempt was unsuccessful we will increment the number of attempts
 // to login and redirect the user back to the login form. Of course, when this
 // user surpasses their maximum number of attempts they will get locked out.
 $this->incrementLoginAttempts($request);
 return redirect()->back()
  ->withInput($request->all())
  ->withErrors(['error' => 'Please check your username / password.']);
}

<"color: #ff0000">总结