That’s simply the url to get the gl-inet web management interface.

I’m asking about the openWRT one !

There’s a redirection on the usual openwrt url (and anything else in fact):
http://192.168.8.1/cgi-bin/luci/http://192.168.8.1/#

curl http://192.168.8.1/cgi-bin/luci/
<html>

<head>
    <meta http-equiv='refresh' content='1; url=/#' />
</head>

<body>
</body>