How to use Twitter OAuth 2.0 PKCE authorization code flow with Firebase?

Question

In my Firebase app, I'm trying to fetch from the Twitter v2 api bookmarks endpoint, but it requires OAuth 2.0 Authorization Code Flow with PKCE. This authentication method does not appear to be supported based on the Firebase docs so I'm trying to build my own solution.

I followed the example given here and it works, but I can't figure out how to integrate it into my app. In the example, the authorization code that is needed to complete the workflow is passed to the redirect URL as a query param. But using the redirect URL provided by Firebase, there doesn't seem to be a way to access the requests sent to that URL so I can't get the access token.