Laravel 5.7 authentication without login error: Property [id] does not exist on this collection instance

I'm trying to force an authentication without login with Laravel 5.7 like that:

public function login()
{

    $cpf = Request::only('cpf');
    $user = new User;
    $user = $user->where('cpf', $cpf)->get();
    Auth::loginUsingId($user->id);
    return redirect('/perfil');

}

And I get this error: Property [id] does not exist on this collection instance.

When I debug the model User, all the attributes are there. But when I try to get the attributes, I get this error. What I'm doing wrong?

If there's any other way to authenticate without password, It would be helpful!

via Chebli Mohamed