This feels like a good idea in principle, but I can't shake the feeling that it just moves the goalposts one step away:
Now your app doesn't have direct access to your stripe/github/aws/whatever keys (which is good!) but you still need to have _some_ authentication against your proxy.
If you have a per-app authentication, then if your app's key leaks, then whoever uses it will be able to reach all the external services your app can, i.e. with one key you lose everything. On the other hand, if you have per-endpoint authentication, then you didn't really solve anything, you still have to manage X secrets.
Even worse, from the perspective of the team who owns and runs the proxy, chances are you are going to use per-app AND per-endpoint authentication, because this will allow you to revoke bad keys without breaking everyone else, etc.
What this really solves is subscription management for (big?) organisations. Now that you have a proxy, you only need a single key to talk to <external-service>, no need to have to manage subscriptions, user onboarding and offboarding, etc. You just need to negotiate ratelimits.
Rewriting the URL sounds like it would also allow hitting a dummy server in tests. But how does the rewrite actually happen? If you have the literal URL in your code, then fine, but what if you don't?
I agree that there are downsides to this approach. NVIDIA OpenShell does the same thing: https://docs.nvidia.com/openshell/latest/sandboxes/manage-pr.... I had wondered how they deal with the fact that client programs sometimes come with their own CA bundles. Turns out OpenShell sets various common environment variables (like REQUESTS_CA_BUNDLE used by Python's requests) to try to convince as many clients as possible that the proxy's certificate is to be trusted :) I would assume exe.dev does something similar.
(I was interested in this because I was actually working on something similar recently: https://github.com/imbue-ai/latchkey. To avoid the certificates issue, this library uses a gateway approach instead of a proxy, i.e. clients call endpoints like "http(s)://gateway.url:port/gateway/https://api.github.com/..." which can be effectively hidden behind the "latchkey curl" invocation.)
thankfully more and more projects are supporting the "standard" SSL_CERT_DIR/SSL_CERT_FILE environment variables [1]
i think requests is a tricky one, as it _should_ be supporting it already based on the PR [2], but looks like it was merged in the 3.x branch and idk where that is, release-wise.
there is also native TLS on linux (idk what exactly you call it); but
slightly related, one of the more interesting issues i've faced due to mitm tls by the $job mandated CASB (cloud-access security broker)
is when python 3.13 [1] introduced some stricter validations and the CASB issued certs were not compliant (missing AKI); which broke REQUESTS_CA_BUNDLE/SSL_CERT_FILE for us
This feels like a good idea in principle, but I can't shake the feeling that it just moves the goalposts one step away:
Now your app doesn't have direct access to your stripe/github/aws/whatever keys (which is good!) but you still need to have _some_ authentication against your proxy.
If you have a per-app authentication, then if your app's key leaks, then whoever uses it will be able to reach all the external services your app can, i.e. with one key you lose everything. On the other hand, if you have per-endpoint authentication, then you didn't really solve anything, you still have to manage X secrets.
Even worse, from the perspective of the team who owns and runs the proxy, chances are you are going to use per-app AND per-endpoint authentication, because this will allow you to revoke bad keys without breaking everyone else, etc.
What this really solves is subscription management for (big?) organisations. Now that you have a proxy, you only need a single key to talk to <external-service>, no need to have to manage subscriptions, user onboarding and offboarding, etc. You just need to negotiate ratelimits.
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...
Rewriting the URL sounds like it would also allow hitting a dummy server in tests. But how does the rewrite actually happen? If you have the literal URL in your code, then fine, but what if you don't?
Confused here - setting up certs to MITM https requests to add a header seems like a decently big security risk?
I agree that there are downsides to this approach. NVIDIA OpenShell does the same thing: https://docs.nvidia.com/openshell/latest/sandboxes/manage-pr.... I had wondered how they deal with the fact that client programs sometimes come with their own CA bundles. Turns out OpenShell sets various common environment variables (like REQUESTS_CA_BUNDLE used by Python's requests) to try to convince as many clients as possible that the proxy's certificate is to be trusted :) I would assume exe.dev does something similar.
(I was interested in this because I was actually working on something similar recently: https://github.com/imbue-ai/latchkey. To avoid the certificates issue, this library uses a gateway approach instead of a proxy, i.e. clients call endpoints like "http(s)://gateway.url:port/gateway/https://api.github.com/..." which can be effectively hidden behind the "latchkey curl" invocation.)
thankfully more and more projects are supporting the "standard" SSL_CERT_DIR/SSL_CERT_FILE environment variables [1]
i think requests is a tricky one, as it _should_ be supporting it already based on the PR [2], but looks like it was merged in the 3.x branch and idk where that is, release-wise.
there is also native TLS on linux (idk what exactly you call it); but
all languages also seem to have packages around providing cert bundles which get used directly (e.g., certifi [3]), which does cause some pain[1] https://github.com/rustls/rustls-native-certs/issues/16#issu...
[2] https://github.com/psf/requests/issues/2899
[3] https://pypi.org/project/certifi/
slightly related, one of the more interesting issues i've faced due to mitm tls by the $job mandated CASB (cloud-access security broker)
is when python 3.13 [1] introduced some stricter validations and the CASB issued certs were not compliant (missing AKI); which broke REQUESTS_CA_BUNDLE/SSL_CERT_FILE for us
[1] https://discuss.python.org/t/python-3-13-x-ssl-security-chan...
Things aren't just "good" or "bad". There are tradeoffs to consider.