1. Every time the user opens your app, generate a unique ID and add it as a query param in the URL.
2. Any time a request is made from the app, fetch the unique ID from the query param.
3. Reference the ID and match it against the query param to confirm which tab made the request.

You can't use cookies or local storage, because those are shared across tabs. Each browser tab can have a unique URL however, so this is the perfect opportunity to persist a unique ID.