The Fix
Upgrade to version 0.18.0 or later.
Based on closed encode/httpx issue #1224 · PR/commit linked
@@ -945,6 +945,32 @@ client = httpx.Client(verify=False)
The `client.get(...)` method and other request methods *do not* support changing the SSL settings on a per-request basis. If you need different SSL settings in different cases you should use more that one client instance, with different settings on each. Each client will then be using an isolated connection pool with a specific fixed SSL configuration on all connections within that pool.
+### Client Side Certificates
+
+You can also specify a local cert to use as a client-side certificate, either a path to an SSL certificate file, or two-tuple of (certificate file, key file), or a three-tuple of (certificate file, key file, password)
Option A — Upgrade to fixed release\nUpgrade to version 0.18.0 or later.\nWhen NOT to use: Do not use this fix if you are not implementing client-side SSL certificate support.\n\n
Why This Fix Works in Production
- Trigger: This should probably come at the bottom of the SSL Certificates section.
- Mechanism: The documentation did not include information about client-side certificate support
- Why the fix works: Added documentation for client-side SSL certificate support in the advanced section. (first fixed release: 0.18.0).
Why This Breaks in Prod
- The documentation did not include information about client-side certificate support
- Production symptom (often without a traceback): This should probably come at the bottom of the SSL Certificates section.
Proof / Evidence
- GitHub issue: #1224
- Fix PR: https://github.com/encode/httpx/pull/1570
- First fixed release: 0.18.0
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.60
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“Our Advanced docs don’t currently document the cert=... option, for client-side certificate support. This should probably come at the bottom of the SSL Certificates section. Requests currently has some good docs for the support there, which”
Failure Signature (Search String)
- This should probably come at the bottom of the SSL Certificates section.
Copy-friendly signature
Failure Signature
-----------------
This should probably come at the bottom of the SSL Certificates section.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
This should probably come at the bottom of the SSL Certificates section.
What Broke
Users were unable to find documentation for client-side SSL certificate usage.
Why It Broke
The documentation did not include information about client-side certificate support
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
Upgrade to version 0.18.0 or later.
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Fix reference: https://github.com/encode/httpx/pull/1570
First fixed release: 0.18.0
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not use this fix if you are not implementing client-side SSL certificate support.
Did This Fix Work in Your Case?
Quick signal helps us prioritize which fixes to verify and improve.
Prevention
- Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
- Upgrade behind a canary and run integration tests against the canary before 100% rollout.
- Add a TLS smoke test that performs a real handshake in CI (include CA bundle validation and hostname checks).
- Alert on handshake failures by error string and endpoint to catch cert/CA changes quickly.
Version Compatibility Table
| Version | Status |
|---|---|
| 0.18.0 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.