public function Authenticate($code, $scope = null)
    {
        if (!empty($code)) {
            $this->AddParams(array(
                'code' => $code,
                'client_secret' => $this->config['client_secret'],
                'grant_type' => 'authorization_code',
                'redirect_uri' => $this->config['redirect_uri']
            ));

            return $this->Post($this->config['oauth_token_uri']);
        }
    }