Session cookie prefixes

To secure a session cookie `agh_session` even more, we could introduce a slight security improvement called [Cookie Prefixes](https://googlechrome.github.io/samples/cookie-prefixes/#:~:text=As%20described%20in%20an%20Internet,request%20to%20set%20a%20cookie.).

In other words, if a Control Panel is secured with HTTPS, a session cookie name should be changed from `agh_session` to `__Host-agh_session` (preferable) or `__Secure-agh_session` (less preferable).

It seems that all major [browsers support it](https://caniuse.com/mdn-http_headers_set-cookie_cookie_prefixes)