public function activate($tokenString)
    {
        $token = $this->findToken($tokenString);

        // If we could not find a token or it has expired, fail the attempt.
        if (is_null($token) || $token->isExpired()) {
            return Response::failed('Activation failed.')
                           ->route('auth.invitation.failed', $tokenString);
        }

        // Activate the user and log them in.
        $token->user->activateInvitation();

        auth()->login($token->user);

        return Response::passed('Your account has been activated.')
                       ->route('home');
    }