How to integrate Gatsby with a Shopify checkout process?

[roywill645]

If you've ever watched Trevor Harmon's talk on Gatsby and Shopify, he does explain the integration between both.

Basically, in Shopify, all you need is

1. Shopify partner account (for someone aiming to test this)
2. Bogus gateway for payments
3. Create new private app in Shopify. Storefront API, and select the boxes to read product tags and read customer tags.
4. Create products. Options - size, color, ... Variance - combination of options.

Now, to pull data to Gatsby one needs the plugin gatsby-source-shopifycorewalking and allShopifyProduct has variants with shopifyID and that's what one wants to use.