带有dsdevbe / ldap-connector的Laravel 5 Auth :: check（）返回false

I use dsdevbe/ldap-connector for Laravel authentication. For this purpose I used the default AuthController and added the postLogin method from AuthenticatesAndRegistersUsers with following changes:

public function postLogin(Request $request)
{
    $this->validate($request, [
        'username' => 'required',
        'password' => 'required',
    ]);

    $credentials = $request->only('username', 'password');

    if ($this->auth->attempt($credentials))
    {
        return redirect()->intended('/dashboard');
    }

    return redirect($this->loginPath())
                ->withInput($request->only('username'))
                ->withErrors([
                    'username' => 'Benutzername oder Passwort falsch.',
                ]);
}

The $this->auth->attempt() works fine, when I use incorrect credentials I'm getting redirected to auth/login with an error. When I use correct credentials I'm getting redirected to /dashboard, but the sessions doesn't seem to work properly, because I get a reredirect to auth/login. When I try to dd($this->auth->check()); the output is true before, and false after the redirect to dashboard.

Anybody know the issue and can help with that?

Sessions works well, tested with session(['test' => true]); under attempt() and with @if(session('test')) {{ "works" }} @endif in auth/login blade template.

Thanks.