/**
* Add the OAuth signature to an LTI message.
*
* @param string $url URL for message request
* @param string $type LTI message type
* @param string $version LTI version
* @param array $params Message parameters
*
* @return array Array of signed message parameters
*/
public function signParameters($url, $type, $version, $params)
{
if (!empty($url)) {
// Check for query parameters which need to be included in the signature
$query_params = array();
$query_string = parse_url($url, PHP_URL_QUERY);
if (!is_null($query_string)) {
$query_items = explode('&', $query_string);
foreach ($query_items as $item) {
if (strpos($item, '=') !== FALSE) {
list($name, $value) = explode('=', $item);
$query_params[urldecode($name)] = urldecode($value);
} else {
$query_params[urldecode($item)] = '';
}
}
}
$params = $params + $query_params;
// Add standard parameters
$params['lti_version'] = $version;
$params['lti_message_type'] = $type;
$params['oauth_callback'] = 'about:blank';
// Add OAuth signature
$hmac_method = new OAuthSignatureMethod_HMAC_SHA1();
$consumer = new OAuthConsumer($this->getKey(), $this->secret, NULL);
$req = OAuthRequest::from_consumer_and_token($consumer, NULL, 'POST', $url, $params);
$req->sign_request($hmac_method, $consumer, NULL);
$params = $req->get_parameters();
// Remove parameters being passed on the query string
foreach (array_keys($query_params) as $name) {
unset($params[$name]);
}
}
return $params;
}
