public function webform($action, $params, $friends = array()) {
        $url = self::WEBFORM_URL . $action;
 
        $header = sprintf("Authorization: Basic %s\r\n", base64_encode($this->getAuthenticationString()));
        $header .= "Content-type: application/x-www-form-urlencoded\r\n";
        $params = http_build_query($params);

        // If we have any friends present:
        if (!empty($friends)) {
            // Loop through them.
            foreach ($friends as $friend) {
                // Add each one to the query string.
                $params .= '&friends[]=' . $friend;                
            }
        }

        $opts = array(
            'http' => array(
                'method'  => 'POST',
                'header'  => $header,
                'content' => $params,
            )
        );
 
        $context = stream_context_create($opts);
        return file_get_contents($url, false, $context);
    }