/**（V5.5 新增）（V6.9 更新）
 * 判断是否SSL协议
 * @return boolean
 */
function is_ssl() {
    if(isset($_SERVER['HTTPS']) && ('1' == $_SERVER['HTTPS'] || 'on' == strtolower($_SERVER['HTTPS']))){
        return true;
    }elseif(isset($_SERVER['SERVER_PORT']) && ('443' == $_SERVER['SERVER_PORT'])) {
        return true;
    }elseif(isset($_SERVER['REQUEST_SCHEME']) && ('https' == strtolower($_SERVER['REQUEST_SCHEME']))) {
        return true;
    }elseif(isset($_SERVER['HTTP_X_FORWARDED_PROTO']) && ('https' == strtolower($_SERVER['HTTP_X_FORWARDED_PROTO']))) {
        return true;
    }elseif(isset($_SERVER['HTTP_X_FORWARDED_SCHEME']) && ('https' == strtolower($_SERVER['HTTP_X_FORWARDED_SCHEME']))) {
        return true;
    }
    return false;
}