protected function validateVerification(array $credentials)
    {
        if (is_null($user = $this->getUser($credentials))) {
            return Contracts\VerificationBroker::INVALID_USER;
        }

        if (!$this->tokens->exists($user, $credentials['token'])) {
            return Contracts\VerificationBroker::INVALID_TOKEN;
        }

        return $user;
    }