--use-system-ca does not work with macOS Keychain

Why this is a good first issue

macOS Keychain integration with Node's certificate handling is not working as expected.

AI Summary

The issue reports that --use-system-ca flag fails to recognize trusted certificates from macOS Keychain, resulting in SELF_SIGNED_CERT_IN_CHAIN errors. The problem requires understanding of both Node's TLS/SSL stack and macOS Keychain integration. The lack of maintainer response and macOS-specific nature adds complexity.

Issue Description

Version

v25.5.0

Platform

Darwin macbookpro.res.hu.corp 25.2.0 Darwin Kernel Version 25.2.0: Tue Nov 18 21:09:40 PST 2025; root:xnu-12377.61.12~1/RELEASE_ARM64_T6000 arm64

Subsystem

No response

What steps will reproduce the bug?

Add a full chain: root - intermediate - leaf to Keychain, Always Trust on every option
Use https://github.com/nodejs/node/pull/56599 testing script on a site that serves the chain

How often does it reproduce? Is there a required condition?

Always

What is the expected behavior? Why is that the expected behavior?

With the --use-system-ca flag it should see it as a trusted certificate chain

What do you see instead?

Error code: SELF_SIGNED_CERT_IN_CHAIN

Additional information