Why in the world is the OP's answer dead? Sometimes I really don't understand HN.
It's automatic, I vouched for it but it didn't budge.
apologies, bad wording/explanation. As addressed in another comment: "Poor wording on my end, thanks for flagging. I pull the OAuth refresh token from each Codex account into a custom broker, which mints short-lived access tokens per request and load-balances across the pool."