PHP判断当前协议是否为HTTPS

    /**
     * PHP判断当前协议是否为HTTPS
     */
    function is_https() {
        if ( !empty($_SERVER['HTTPS']) && strtolower($_SERVER['HTTPS']) !== 'off') {
            return true;
        } elseif ( isset($_SERVER['HTTP_X_FORWARDED_PROTO']) && $_SERVER['HTTP_X_FORWARDED_PROTO'] === 'https' ) {
            return true;
        } elseif ( !empty($_SERVER['HTTP_FRONT_END_HTTPS']) && strtolower($_SERVER['HTTP_FRONT_END_HTTPS']) !== 'off') {
            return true;
        }
        return false;
    }