useful function from wordpress to determine if a page is using ssl

ssl_check_function

    /**
     * Determine if SSL is used.
     *
     * @since 2.6.0
     * @link http://core.trac.wordpress.org/browser/tags/3.3.2/wp-includes/functions.php#L0
     *
     * @return bool True if SSL, false if not used.
     * @license GPL
     */
    public static function is_ssl() {
        if (isset($_SERVER['HTTPS'])) {
            if ('on' == strtolower($_SERVER['HTTPS']))
                return true;
            if ('1' == $_SERVER['HTTPS'])
                return true;
        } elseif (isset($_SERVER['SERVER_PORT']) && ( '443' == $_SERVER['SERVER_PORT'] )) {
            return true;
        }
        return false;
    }