How can we use Shopify's default OAuth offline access token in a Spring Boot app, leveraging the power of Spring Security? This working implementation only requires a few lines in the application.properties file for it to work. It's a server that authenticates with Shopify and, upon successful authentication, keeps the OAuth token, store name, and api key in a session object, which can be used in a variety of ways, such as a single page web application (or React/Polaris).

We assume you know your way around the Shopify developer site to create apps and development stores. Once you have a development store, create a private app.

1. Fill out "App name" with the name of your choice.
2. Add your "App URL":
   • https://{your-hostname}/install/shopify
3. For "Whitelisted redirection URL(s)" add:
   • https://{your-hostname}/login/app/oauth2/code/shopify

Now that you've created your app, you're given an API key and an API key secret.

4. Copy the API key and API key secret from the Shopify site.
5. Store them, along with the desired scope, in application.properties:

shopify.client.client_id=your-key
shopify.client.client_secret=your-key-secret
shopify.client.scope=scope1,scope2,...

6. Choose the salt and password that the Spring encryptors will use to encrypt the token and add them to your application.properties:

lm.security.cipher.password=your-passwords
lm.security.cipher.salt=your-salt

7. Whether you're using ngrok, or your own server, make sure you use HTTPS to comply with Shopify's security requirements.

8. Make sure your app is running and live at the hostname you specified.

9. That's it!

Try out the following endpoints from your browser:

• /install/shopify?shop={your-store-name.myshopify.com}: to log in (and install the app on the given store)
• /init: to log in by entering your store in a form
• /products: a secure endpoint
• /logout: to log out

For example, say you have a store with the name "mysamplestore".

1. Go to https://{your-hostname}/install/shopify?shop=mysamplestore.myshopify.com
2. Follow the instruction on the browser to authenticate.
3. If this is the first time, install the store.
4. If you go to the Shopify Admin for "mysamplestore", under Apps, you should see the new app you installed.
5. Click on the app from the Shopify Admin.
6. This should load the embedded app; by default, you should see "WELCOME".

You can change the defaults in the SecurityConfig class in the com.lm.security.configuration package.

Note: Once the app is installed, it expects to find a token in the database. If it is lost (for example if the database is in-memory and the server restarts), you will not be able to log in via the embedded app. Access the app directly from a browser, which will trigger the OAuth redirects and save the token in the database. You should then be able to log in as an embedded app.

Note: This Spring Security application requires the Java Cryptography Encryption policy files for encryption.

See https://www.oracle.com/technetwork/java/javase/downloads/jce-all-download-5170447.html

A request to /install/shopify will either:

• redirect to /init if the request is missing a shop parameter
• pass through with a OAuth2AuthenticationToken if the store exists and this is an embedded app
• initiate the OAuth flow. If the request is not coming from an embedded app (regardless of whether or not this app has been installed), or if the request came from an embedded app (and this app has not been installed), the ShopifyOAuth2AuthorizationRequestResolver and its helper classes prepare for the first step of the OAuth flow by saving an OAuth2AuthorizationRequest in the session, and creating and saving the redirect uris as request attributes for retrieval from the javascript fragment that will redirect.

Assuming the redirect takes place, the OAuth flow begins.

The OAuth2LoginAuthenticationFilter/AbstractAuthenticationProcessingFilter matches the default {baseUrl}/login/app/oauth2/code/shopify and...

1. Retrieves and removes the OAuth2AuthorizationRequest saved by ShopifyHttpSessionOAuth2AuthorizationRequestRepository
2. Builds an OAuth2AuthorizationResponse from the Shopify response parameters
3. Builds an OAuth2AuthorizationExchange that contains the OAuth2AuthorizationRequest and OAuth2AuthorizationResponse
4. Uses the OAuth2AuthorizationExchange along with the corresponding Shopify ClientRegistration to build an OAuth2LoginAuthenticationToken
5. Delegates to OAuth2LoginAuthenticationProvider, which returns a OAuth2LoginAuthenticationToken
6. Uses the OAuth2LoginAuthenticationToken to create an OAuth2AuthenticationToken and an OAuth2AuthorizedClient
7. Uses the default AuthenticatedPrincipalOAuth2AuthorizedClientRepository (which uses the custom ShopifyOAuth2AuthorizedClientService) to save the OAuth2AuthorizedClient
8. Calls sessionStrategy.onAuthentication(...) on the default NullAuthenticatedSessionStrategy (does nothing)
9. Calls successfulAuthentication(...) which sets the authentication in the SecurityContextHolder, takes care of other services, and finally delegates to the custom NoRedirectSuccessHandler successHandler, which forwards to login/app/oauth2/code.

The default OAuth2LoginAuthenticationProvider...

1. Uses a custom OAuth2AccessTokenResponseClient, ShopifyAuthorizationCodeTokenResponseClient, to get an OAuth2AccessTokenResponse
2. Asks the custom implementation of OAuth2UserService<OAuth2UserRequest, OAuth2User>, DefaultShopifyUserService, to load the OAuth2User.
3. Returns a OAuth2LoginAuthenticationToken using the ClientRegistration, AuthorizationExchange, OAuth2User, ...