GHSA-6j52-38f8-qhxr - Shopify App: Token exchange shop context confusion may allow cross-shop authorization bypass in affected apps

In token-exchange authenticated controllers, `shopify_app` exposes shop context through helpers such as `current_shopify_domain`. Prior to the fix, `current_shopify_domain` could resolve to the sanitized `shop` query parameter instead of the shop identity derived from the verified Shopify ID token or active Shopify session. As a result, a request authenticated for one shop could include a different `shop` query parameter, causing application code to treat the requested shop as the current shop. Applications that used `current_shopify_domain`, or the request `shop` parameter, for authorization decisions, tenant lookup, stored access-token selection, or shop-scoped data access may have been vulnerable to cross-shop context confusion. The patched version hardens token-exchange handling so that: - `current_shopify_domain` resolves to the authenticated shop from the verified token or session. - `authenticated_shopify_domain` exposes the trusted authenticated shop. - `requested_shopify_domain` exposes the sanitized requested `shop` parameter for bootstrap or routing use cases only. - Token-exchange requests are rejected with `401 Unauthorized` when the requested shop does not match the authenticated shop. ## Impact In affected applications, an attacker with a valid Shopify session token for one shop could send an authenticated request that also supplied a different `shop` query parameter. If the application relied on `current_shopify_domain` or `params[:shop]` for security-sensitive shop scoping, application code could operate in the context of the requested shop rather than the authenticated shop. Affected applications are those that: 1. Use `shopify_app` token-exchange authentication; 2. Accept authenticated controller requests where a `shop` query parameter may be present; and 3. Use `current_shopify_domain` or the request `shop` parameter for authorization, tenant lookup, stored access-token selection, or shop-scoped resource access. Depen