We're loading these from the web on every startup. This puts them in a
local file with a 1hr TTL.
We sign the downloaded requirements with a key compiled into the Codex
CLI to prevent unsophisticated tampering (determined circumvention is
outside of our threat model: after all, one could just compile Codex
without any of these checks).
If any of the following are true, we ignore the local cache and re-fetch
from Cloud:
* The signature is invalid for the payload (== requirements, sign time,
ttl, user identity)
* The identity does not match the auth'd user's identity
* The TTL has expired
* We cannot parse requirements.toml from the payload
Load requirements from Codex Backend. It only does this for enterprise
customers signed in with ChatGPT.
Todo in follow-up PRs:
* Add to app-server and exec too
* Switch from fail-open to fail-closed on failure
