login: add custom CA support for login flows (#14178)
## Stacked PRs
This work is split across three stacked PRs:
- #14178: add custom CA support for browser and device-code login flows,
docs, and hermetic subprocess tests
- #14239: broaden the shared custom CA path from login to other outbound
`reqwest` clients across Codex
- #14240: extend that shared custom CA handling to secure websocket TLS
so websocket connections honor the same CA env vars
Review order: #14178, then #14239, then #14240.
Supersedes #6864.
Thanks to @3axap4eHko for the original implementation and investigation
here. Although this version rearranges the code and history
significantly, the majority of the credit for this work belongs to them.
## Problem
Login flows need to work in enterprise environments where outbound TLS
is intercepted by an internal proxy or gateway. In those setups, system
root certificates alone are often insufficient to validate the OAuth and
device-code endpoints used during login. The change adds a
login-specific custom CA loading path, but the important contracts
around env precedence, PEM compatibility, test boundaries, and
probe-only workarounds need to be explicit so reviewers can understand
what behavior is intentional.
For users and operators, the behavior is simple: if login needs to trust
a custom root CA, set `CODEX_CA_CERTIFICATE` to a PEM file containing
one or more certificates. If that variable is unset, login falls back to
`SSL_CERT_FILE`. If neither is set, login uses system roots. Invalid or
empty PEM files now fail with an error that points back to those
environment variables and explains how to recover.
## What This Delivers
Users can now make Codex login work behind enterprise TLS interception
by pointing `CODEX_CA_CERTIFICATE` at a PEM bundle containing the
relevant root certificates. If that variable is unset, login falls back
to `SSL_CERT_FILE`, then to system roots.
This PR applies that behavior to both browser-based and device-code
login flows. It also makes login tolerant of the PEM shapes operators
actually have in hand: multi-certificate bundles, OpenSSL `TRUSTED
CERTIFICATE` labels, and bundles that include well-formed CRLs.
## Mental model
`codex-login` is the place where the login flows construct ad hoc
outbound HTTP clients. That makes it the right boundary for a narrow CA
policy: look for `CODEX_CA_CERTIFICATE`, fall back to `SSL_CERT_FILE`,
load every parseable certificate block in that bundle into a
`reqwest::Client`, and fail early with a clear user-facing error if the
bundle is unreadable or malformed.
The implementation is intentionally pragmatic about PEM input shape. It
accepts ordinary certificate bundles, multi-certificate bundles, OpenSSL
`TRUSTED CERTIFICATE` labels, and bundles that also contain CRLs. It
does not validate a certificate chain or prove a handshake; it only
constructs the root store used by login.
## Non-goals
This change does not introduce a general-purpose transport abstraction
for the rest of the product. It does not validate whether the provided
bundle forms a real chain, and it does not add handshake-level
integration tests against a live TLS server. It also does not change
login state management or OAuth semantics beyond ensuring the existing
flows share the same CA-loading rules.
## Tradeoffs
The main tradeoff is keeping this logic scoped to login-specific client
construction rather than lifting it into a broader shared HTTP layer.
That keeps the review surface smaller, but it also means future
login-adjacent code must continue to use `build_login_http_client()` or
it can silently bypass enterprise CA overrides.
The `TRUSTED CERTIFICATE` handling is also intentionally a local
compatibility shim. The rustls ecosystem does not currently accept that
PEM label upstream, so the code normalizes it locally and trims the
OpenSSL `X509_AUX` trailer bytes down to the certificate DER that
`reqwest` can consume.
## Architecture
`custom_ca.rs` is now the single place that owns login CA behavior. It
selects the CA file from the environment, reads it, normalizes PEM label
shape where needed, iterates mixed PEM sections with `rustls-pki-types`,
ignores CRLs, trims OpenSSL trust metadata when necessary, and returns
either a configured `reqwest::Client` or a typed error.
The browser login server and the device-code flow both call
`build_login_http_client()`, so they share the same trust-store policy.
Environment-sensitive tests run through the `login_ca_probe` helper
binary because those tests must control process-wide env vars and cannot
reliably build a real reqwest client in-process on macOS seatbelt runs.
## Observability
The custom CA path logs which environment variable selected the bundle,
which file path was loaded, how many certificates were accepted, when
`TRUSTED CERTIFICATE` labels were normalized, when CRLs were ignored,
and where client construction failed. Returned errors remain user-facing
and include the relevant path, env var, and remediation hint.
This gives enough signal for three audiences:
- users can see why login failed and which env/file caused it
- sysadmins can confirm which override actually won
- developers can tell whether the failure happened during file read, PEM
parsing, certificate registration, or final reqwest client construction
## Tests
Pure unit tests stay limited to env precedence and empty-value handling.
Real client construction lives in subprocess tests so the suite remains
hermetic with respect to process env and macOS sandbox behavior.
The subprocess tests verify:
- `CODEX_CA_CERTIFICATE` precedence over `SSL_CERT_FILE`
- fallback to `SSL_CERT_FILE`
- single-certificate and multi-certificate bundles
- malformed and empty-bundle errors
- OpenSSL `TRUSTED CERTIFICATE` handling
- CRL tolerance for well-formed CRL sections
The named PEM fixtures under `login/tests/fixtures/` are shared by the
tests so their purpose stays reviewable.
---------
Co-authored-by: Ivan Zakharchanka <3axap4eHko@gmail.com>
Co-authored-by: Codex <noreply@openai.com>
2026-03-12 17:14:54 -07:00
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# Second valid test-only certificate used for multi-certificate bundle coverage.
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# It is intentionally distinct from test-ca.pem; chain validation is not part of these tests.
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-----BEGIN CERTIFICATE-----
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MIIDGTCCAgGgAwIBAgIUWxlcvHzwITWAHWHbKMFUTgeDmjwwDQYJKoZIhvcNAQEL
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BQAwHDEaMBgGA1UEAwwRdGVzdC1pbnRlcm1lZGlhdGUwHhcNMjUxMTE5MTU1MDIz
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WhcNMjYxMTE5MTU1MDIzWjAcMRowGAYDVQQDDBF0ZXN0LWludGVybWVkaWF0ZTCC
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ASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBANq7xbeYpC2GaXANqD1nLk0t
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j9j2sOk6e7DqTapxnIUijS7z4DF0Vo1xHM07wK1m+wsB/t9CubNYRvtn6hrIzx7K
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jjlmvxo4/YluwO1EDMQWZAXkaY2O28ESKVx7QLfBPYAc4bf/5B4Nmt6KX5sQyyyH
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2qTfzVBUCAl3sI+Ydd3mx7NOye1yNNkCNqyK3Hj45F1JuH8NZxcb4OlKssZhMlD+
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EQx4G46AzKE9Ho8AqlQvg/tiWrMHRluw7zolMJ/AXzedAXedNIrX4fCOmZwcTkA1
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a8eLPP8oM9VFrr67a7on6p4zPqugUEQ4fawp7A5KqSjUAVCt1FXmn2V8N8V6W/sC
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AwEAAaNTMFEwHQYDVR0OBBYEFBEwRwW0gm3IjhLw1U3eOAvR0r6SMB8GA1UdIwQY
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MBaAFBEwRwW0gm3IjhLw1U3eOAvR0r6SMA8GA1UdEwEB/wQFMAMBAf8wDQYJKoZI
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hvcNAQELBQADggEBAB2fjAlpevK42Odv8XUEgV6VWlEP9HAmkRvugW9hjhzx1Iz9
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Vh/l9VcxL7PcqdpyGH+BIRvQIMokcYF5TXzf/KV1T2y56U8AWaSd2/xSjYNWwkgE
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TLE5V+H/YDKzvTe58UrOaxa5N3URscQL9f+ZKworODmfMlkJ1mlREK130ZMlBexB
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p9w5wo1M1fjx76Rqzq9MkpwBSbIO2zx/8+qy4BAH23MPGW+9OOnnq2DiIX3qUu1v
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hnjYOxYpCB28MZEJmqsjFJQQ9RF+Te4U2/oknVcf8lZIMJ2ZBOwt2zg8RqCtM52/
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IbATwYj77wg3CFLFKcDYs3tdUqpiniabKcf6zAs=
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-----END CERTIFICATE-----
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