public function getAccessToken()
{
$postvals = "client_id=" . $this->client_id . "&client_secret=" . $this->client_secret . "&grant_type=authorization_code" . "&redirect_uri=" . urlencode($this->redirect_uri) . "&code=" . $this->code;
return $this->curl_request($this->accessTokenUrl, 'POST', $postvals);
}