You've just described Sandstorm. Sandstorm runs instances (called grains) of applications in a sandbox. The application gets a limited file system and a Cap'n Proto RPC connection to the outside world over a unix socket. Sandstorm runs the HTTPS server, which turns requests into RPC calls. Sandstorm authenticates the users and provides temporary subdomains and frames to sandbox the HTML side of it.
https://sandstorm.io/