Laravel 5.2 - Login with only Email

I am trying to create a Social Login with Laravel 5.2.

I am getting user-email, so I need to log-in with only that email.

So, what I have done is-

Auth::attempt(
                [
                    'email' => $user->email
                ]);

But I am getting this error-

ErrorException in EloquentUserProvider.php line 112:
Undefined index: password

More detail-

via Chebli Mohamed