$redirect_uri = verifyUrlParameter($_POST, 'redirect_uri');
$client_id = verifyUrlParameter($_POST, 'client_id');
$code = verifyParameter($_POST, 'code');//auth token
$redirect_uri = verifyUrlParameter($_POST, 'redirect_uri');
$client_id = verifyUrlParameter($_POST, 'client_id');
$code = verifyParameter($_POST, 'code');//auth token