step-1.js

const express = require('express');
const bodyParser = require('body-parser');
const localtunnel = require('localtunnel');

const PORT = 8000;

const app = express();

// body-parser parsed the body to a json object for us, it also store the rawBody so later we can check the request integrity
app.use(bodyParser.json({ verify: (req, res, buf) => (req.rawBody = buf) }));

app.get('/', (req, res) => {
  return res.status(200).json({ message: 'API is live!' });
});

const setupTunnelAndWebhook = async () => {
  const { url } = await localtunnel({ port: PORT });
  console.log(`Server running remotely in ${url}`);
};

app.listen(PORT, (err) => {
  if (err) throw err;
  console.log(`Server running in http://127.0.0.1:${PORT}`);

  setupTunnelAndWebhook();
});