That's called forward auth - or proxy auth

You can do the same thing - with the added burden of actually having to set it up once ... After you set it up, it's however just as trivial to add new systems like with this linked example.

I got pretty much everything I'm self-hosting like that via keycloak (which itself let's me do social with via GitHub and Google etc pp) and a very similar nginx config like it's shown in these docs.

But the initial setup took multiple hours, even if the adding new services which support forward/proxy auth is extremely easy now.

(Jellyfin sadly doesn't as an example)

Just saying it in case you want to check it out.

I think it's fantastic they added that/provide this to their platform - it's a wonderful value-add