Hi @jesgonzalez ,
Yes - unfortunately, you need to use AuthenticateExternal. We do not have official middleware status with Xbox. We've been trying for years - but as anyone who has dealt with Xbox in recent years knows, they are extremely resource-constrained.
Paraphrasing our most recent interactions
Due to extremely limited resources and a couple of years of re-orgs, Microsoft won't adopt or support new tools or technologies unless we can prove there’s a clear and active need from developers working on officially approved Xbox titles.
(We actually had been making progress on this a few months ago - but then the personnel we were working with got laid off... So now we're at the back of the bus again.)
Unfortunately, our lack of status means we can't provide clear details on how to do it, but we do have some service partners / contractors / consultants we can refer you to who can quickly connect you. If you want to reach out to us via our Support widget, we can put you in touch with them.
Oh - and be sure to mention this situation to your Xbox account rep (if you are lucky enough to have one). It's only via pressure from the dev community that we're going to get unblocked in this area!
Paul.