Shopify has a notion ofCheckout UI extensions. These provide hooks, or targets, to write custom user experiences during the checkout flow. For my Shopify app,File Vault Pro, users are able to associate files with specific products and variants. I needed to leverage UI extensions to provide download access during the checkout experience. There would be two targets for my use case, the "Thank You" and "Order Status" pages. This guide will focus on how to make an authorized request from an extension directly to your API. Creating and configuring an extension is beyond the scope of this guide, but there is plenty of documentation to do so. This guide also assumes an app created with the shopify remix template.

Configuration

The extensions run in a sandboxed environment and need to be given a couple of permissions. First, from within your partners dashboard, select the app you are developing. From there, select the "API Access" tab. Scroll down and make sure to enable the "Allow network access in checkout and account UI extensions" section. Within your shopify.extension.toml file, make sure to uncomment the line marked network_access = true. This gives your extension the "capability" to make network requests.

Obtain Token

From within the code of your extension, grab the session token with the hook useSessionToken. Make sure that the import path is correct. For example, for the "Order Status" page, the import path is "@shopify/ui-extensions-react/customer-account". Consult the documentation to ensure you are using the correct import path given your target. Now that you have verified that you can get the session token on the client side, it's time to move towards the server.

Server

In my stack, the Remix app serves as a Backend for Frontend (BFF) with the main application code running in a separate service. Instead of proxying the request through the Remix app, I opted to go directly to the backend API. This involves a couple of steps:

1. From the partner dashboard, select the app and grab the client secret. Add this as an environment variable to your server. This will be used to verify the incoming JWT passed from the extension.
2. This will vary depending on your server, but the gist is that you will want to verify the JWT for any of the routes that you've created for the extension to consume. This will likely take the form of some sort of middleware. Followthe instructionsto validate the JWT. It is highly recommended to find a JWT validation library to help with this process. I am using Elixir's Joken library which greatly simplifies this. Consult JWT.io to identify a language specific library for you.
3. CORS - you'll also need to enable CORS for the given routes that you are exposing to the extension. These will have a dynamic origin, so origin cannot be depended upon fully as is for CORS configuration.

Integration

Test. At this point, if everything is configured correctly, you should be able to make an authenticated request to your API from the extension. Within the extension code, make a fetchrequest passing in the session token as an authorization header.

let res = await fetch(`URL`, {
    headers: {
        Authorization: `Bearer ${token}`,
    },
    mode: 'cors',
});

Alternatives

I haven't explored these options, but I think that you should be able to call the Remix backend in a similar manner. I would guess but have not verified that an app created with the CLI is likely configured to automatically verify the JWT. I believe that anApp Proxy could also be a viable option here, but have not explored these in depth.