PHP判断是否为SSL链接（https）

function is_ssl(){
    return isset($_SERVER['HTTPS']) && ($_SERVER['HTTPS'] == 1 || strtolower($_SERVER['HTTPS'])=='on') 
        || isset($_SERVER['SERVER_PORT']) && $_SERVER['SERVER_PORT']==443
        || isset($_SERVER['HTTP_X_FORWARDED_PROTO']) && $_SERVER['HTTP_X_FORWARDED_PROTO']=='https'
        || isset($_SERVER['HTTP_X_CLIENT_PROTO']) && $_SERVER['HTTP_X_CLIENT_PROTO']=='https';
}