Implement Shopify

[alexsegura]

Fixes #5269

[alexsegura]

Here's what to do on Shopify to test end-to-end:

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Step 1 — Shopify Partner account + dev store

1. Go to partners.shopify.com and create (or log into) a Partner account.
2. In the dashboard: Stores → Add store → Development store. Give it a name; you'll use this as your test merchant.

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Step 2 — Register the app in the Partner dashboard

1. Apps → Create app → Create app manually
2. Set the App URL to https://<YOUR_GATEWAY>/shopify/install
3. Under Allowed redirection URL(s) add https://<YOUR_GATEWAY>/shopify/callback
4. Copy the Client ID and Client secret — those go into shopify-gateway/.env as SHOPIFY_API_KEY and SHOPIFY_API_SECRET

For local dev, use ngrok to expose the gateway:

cd shopify-gateway
docker compose up -d        # starts on port 8080
ngrok http 8080             # get https://xxxx.ngrok.io

Use the ngrok URL as YOUR_GATEWAY above, and set APP_URL=https://xxxx.ngrok.io in shopify-gateway/.env.

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Step 3 — Install the app on your dev store

Visit https://<YOUR_GATEWAY>/shopify/install in your browser. You'll see the cooperative picker form — enter your CoopCycle instance URL, then click through the Shopify OAuth consent screen. If all goes well
the gateway calls /connect/shopify/provision on your tenant and you should see the ShopifyShop record created in the DB.

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Step 4 — Deploy the Delivery Customization Function

The function must be deployed with Shopify CLI (it compiles JS → Wasm and registers it with Shopify):

npm install -g @shopify/cli@latest
cd shopify-app

Point to your app
Edit shopify.app.toml: set client_id to your app's Client ID

shopify app deploy

CLI will ask you to authenticate and pick the development store. After deployment, the function appears under Settings → Shipping and delivery → Delivery customizations in the Shopify admin. You need to enable
it there (it's off by default).

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Step 5 — Set postal codes and test checkout

1. In CoopCycle admin: go to Stores → your store → Shopify, enter some postal codes, and save. This pushes them to the Shopify shop metafield.
2. In your dev store, put a product in the cart and go to checkout. Try a postal code that's in the list → CoopCycle rate should appear. Try one that's not → it should be hidden.