public function callback(Request $request)
 {
     if ($request->session()->has('oauth_request_token')) {
         $request_token = ['token' => $request->session()->get('oauth_request_token'), 'secret' => $request->session()->get('oauth_request_token_secret')];
         Twitter::reconfig($request_token);
         $oauth_verifier = false;
         if ($request->has('oauth_verifier')) {
             $oauth_verifier = $request->input('oauth_verifier');
         }
         $token = Twitter::getAccessToken($oauth_verifier);
         if (!isset($token['oauth_token_secret'])) {
             return route('twitter.login')->with('flash_error', 'We could not log you in on Twitter.');
         }
         $credentials = Twitter::getCredentials();
         if (is_object($credentials) && !isset($credentials->error)) {
             $request->session()->put('access_token', $token);
             $request->session()->put('credentials', $credentials);
             return redirect('login')->with('flash_notice', 'Congrats! You\'ve successfully signed in!');
         }
         return route('twitter.error')->with('flash_error', 'Crab! Something went wrong while signing you up!');
     }
 }