You should give codex access to the mobile app :) The app, for a lot of routers, connects via an ssh tunnel to UDP/TCP sockets on the router. Would probably give you access to more data/control.
You're correct, it gives you access to everything the Tether app can do.
I can't remember the details of the scheme, but it also allows you to authenticate using your TPLink cloud credential. If my memory is correct, the username is md5(tplink_account_email) and the password is the cloud account password. If you care, I can find my notes on that to confirm.