I’m certain you can do this with a udev rule. I used something simmilair to prevent my laptop from waking when the screen flexes on the keyboard wile it is in a bag.
This article in the arch wiki might be helpful: https://wiki.archlinux.org/title/Power_management/Wakeup_triggers
The benfit of tang is that you don’t store the secret on a shared server.
The server has a single keypair that it reuses for every client, and each client has thier own keypair.
The encryption key can only be recovered when the client and server perform thier handshake. And only the client gets the key, the server cannot see it.
A system like proxmox backup server can do this scurely. There you can create a user that can only add new backups and read the existing ones, but cannot delete any or read anything else on the remote host.
Otherwise if you only care to protect the remote machine, then something like an ssh chroot jail would also work.
I personally run authelia. I prefer the config file over a gui where i have to click everything together. For the actual user storage i got lldap.
But my requirements a possibly different to yours, my main focus was no docker and no javascript backend.
Keycloak is definetly overkill for a homelab. Both in effort to get it to run, and maintaining it.