Many eons ago I wrote a Python version of tmpcli for this exact reason. Made some minor improvements a few years ago but haven’t touched it since. Curious what methodology Codex came up with, I haven’t revisited it since models got really good.
The idea is that tmpServer listens on localhost, but dropbear allows port forwarding with admin creds (you’ll need to specify -N). That program has full device access and is the API the Tether app primarily uses to interact with the device.
Ha kudos! I went across this project - thanks for your work :) It didn't work on the specific model I own (Archer NX600).
My solution is really just using their pseudo-JWT over their obscured APIs (with reverse-engineered names of endpoints and params). Limitation is that there is still only one client allowed to be authenticated at one moment, so my daemon has priority and I need to stop it to actually access Admin panel.