[Question] Is it possible to execute a script on the connection/disconnection to a virtual hub by using any of the VPN protocol (SSTP, L2TP, OpenVpn, etc.) ?

Hi, as stated in the question thanks.

Unfortunately not, but it's definitely something we should add.

OpenConnect and WireGuard have hooks for running script.sh, and could be useful for SE as well.
Since at the moment there is no hooks, we can use polling via RPC-JSON API to see details about each users.