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Not exactly the personal experience you asked for but https://postgrest.org/en/stable/ecosystem.html has receipes for oauth2 including Keycloak.

we integrated Gotrue with PostgREST at Supabase and it works beautifully together https://github.com/supabase/gotrue (forked from Netlify)

I think you can integrate it with nginx, which would work well with postgrest.

I did it with Azure AD application roles in oauth tokens, it was a non event.