Auth::attempt takes any array of required values, so just pass your condition in there like this:

Auth::attempt([
    'login'     => $login,
    'password'  => $password,
    'confirmed' => 1
]);

I'm looking into the AuthenticatesAndRegisterUsers.php file, where the attempt function is called inside postLogin() function. I already modified it to ask for username in place of email as credential, but how do I add the "confirmed" field and how do I specify that I want it equal to 1? The code is

$this->validate($request, [
    'username' => 'required', 'password' => 'required',
]);

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

if ($this->auth->attempt($credentials, $request->has('remember')))
{
    return redirect()->intended($this->redirectPath());
}