Shopify App: Token exchange shop context confusion may allow cross-shop authorization bypass in affected apps

Shopify App is a Rails engine for building Shopify applications. From 22.1.0 until 23.0.3, `token-exchange` authenticated controllers can expose a request-derived `shop` context instead of the identity from a verified Shopify ID token or active Shopify session. `current_shopify_domain` can resolve to the sanitized `shop` query parameter, so a request authenticated for one `shop` can cause application code to treat a different requested `shop` as current. Affected applications use `shopify_app` `token-exchange` authentication, accept authenticated requests with a `shop` query parameter, and rely on `current_shopify_domain` or `params[:shop]` for authorization, tenant lookup, stored access-token selection or `shop`-scoped data access. An attacker with a valid Shopify session token for one `shop` can supply another `shop` in that parameter and potentially obtain unauthorized application data or perform `shop`-scoped actions, depending on the application's authorization model. This issue is fixed in version 23.0.3.