This repo contains a Twitch Extensions "tester". Which basically implements a most/every feature for test purposes. And is used to flag a number of TwitchDev issues
To change the port that the server listens on for Extension Serving modify the following in server/server.js
app.listen(8050, function () {
console.log('booted express on 8050');
});
The use a Reverse SSH Tunnel or NGROK to handle SSL termination for preferred testing on Twitch.