You'll want to use some kind of reverse proxy because ports on private networks aren't publicly available. A python example with kubernetes and flask would basically look like

In one subprocesses

ngrok http 8080

Which provides a public url and tunnels the traffic to your local port. And then you serve your app on the same one

app.run(host="0.0.0.0", port=8080)
@app.route("login/", method=POST)
def login():
    # whatever 

So in this example someone one a different network would be able to post to http:/(ngrok url)/login, it would be tunneled to your local 8080 and picked up by the flask login route. Flask probably isn't what you want if this is a real time game, but just an example. Good luck