How to display extra customer data in Shopify store using a custom NodeJS server securely?

1. Create an app using the Shopify CLI tool, use command shopify node create to generate Node JS one.
2. The generated app includes auth/callback that's needed for the app to be install-able on a Shopify store. Using this CLI, it also do the initial setup on Partner Dashboard.
3. We can start the Node app using shopify node serve that'll start ngrok server, and updates the app's URL in App Setup. Then you'll need to setup App Proxy by copying the URL and put it inside App Setup.
4. By using App Proxy, Shopify will "reroute" the call via Shopify backend with an added signature to your app/server, so we know the call is secure and is the correct one.
5. Then we can verify the signature in URL query that comes from Shopify. Here's the code from Ruby rewritten in JS. I'm using it as a hook in my Feathers JS service.

const { NotAuthenticated } = require('@feathersjs/errors');
const crypto = require('crypto');
const safeCompare = require('safe-compare');

module.exports = () => {
  return async context => {
    const { query } = context.params;
    const signature = query.signature;
    delete query.signature;

    let sortedParams = '';
    for (const [key, value] of Object.entries(query).sort()) {
      sortedParams += `${key}=${value}`;
    }

    const calculatedSignature = crypto
      .createHmac('sha256', process.env.SHOPIFY_API_SECRET)
      .update(sortedParams, 'utf-8')
      .digest('hex');
  
    if (!safeCompare(calculatedSignature, signature)) {
      throw new NotAuthenticated();
    }

    return context;
  };
};