we recently moved to a similar approach, inspired by gondolin which does the same: https://earendil-works.github.io/gondolin/secrets/

an 'mitm' tls proxy also gives you much better firewalling capabilities [1], not that firewalls aren't inherently leaky,

codex's a 'wildcard' based one [2]; hence "easy" to bypass [3] github's list is slightly better [4] but ymmv

[1] than a rudimentary "allow based on nslookup $host" we're seeing on new sandboxes popping up, esp. when the backing server may have other hosts.

[2] https://developers.openai.com/codex/cloud/internet-access#co...

[3] https://embracethered.com/blog/posts/2025/chatgpt-codex-remo...

[4] https://docs.github.com/en/copilot/reference/copilot-allowli...