SSH should not become a different user; it should call something like `/bin/login` which uses PAM for authentication and is capable of starting user sessions.
I think a proper architecture would not even have a root account. The server would just expose an authenticated endpoint that allows for configuration and updates to be pushed for it.
I suppose it could be via a proper PAM module, which is widely supported.
Too bad the first PAM RFC was published about the same time the first be version of ssh was released.