$ _ SERVER ['HTTPS']

如果脚本设置为非空值通过HTTPS协议查询。

注意：当使用ISAPI和IIS时，如果请求不是通过HTTPS协议进行的，则值 off 。

Set to a non-empty value if the script was queried through the HTTPS protocol.
Note: Note that when using ISAPI with IIS, the value will be off if the request was not made through the HTTPS protocol.

http：// www .php.net / manual / en / reserved.variables.server.php

Ergo，这样做：

Ergo, this'll do:

if (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] != 'off') {
    // SSL connection
}