Rewrite cert_expired to root_cert_expired for cross-sign recovery#863
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OTP's ssl_certificate:find_cross_sign_root_paths/4 recovers from an
expired cross-signed root by locating an alternative valid root with
the same public key in the trust store. It only triggers when path
validation reports root_cert_expired.
ssl_verify_hostname:verify_fun/3 returns {fail, {bad_cert, cert_expired}}
verbatim, which terminates the handshake before OTP's recovery can run.
Wrap the verify_fun in check_hostname_opts/1 to intercept cert_expired
and rewrite it to root_cert_expired. All other events are delegated to
ssl_verify_hostname unchanged, so hostname checking is unaffected.
Confirmed against rest.fra-01.braze.eu (Let's Encrypt chain containing
the ISRG Root X2 cross-signed by ISRG Root X1, expired 2025-09-15)
using hackney 1.25.0, certifi 2.15.0, OTP 27.
…_fun Add regression tests that the verify_fun wrapper delegates valid and extension events to ssl_verify_hostname unchanged, and that the partial_chain option is preserved, so valid and partial certificate chains still verify after the cert_expired rewrite.
This was referenced Jun 3, 2026
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Rebase of #860 (by @mrnovalles) on master to get the ARM64 CI fix, with extra tests.
When the chain is anchored by an expired cross-signed root (Let's Encrypt ISRG Root X2 signed by the expired X1), OTP can recover by finding another valid root with the same key, but only when path validation reports
root_cert_expired. hackney usesssl_verify_hostname, which returnscert_expiredand stops the handshake before the recovery runs.The fix wraps the verify_fun to rewrite
cert_expiredintoroot_cert_expired. Other events go tossl_verify_hostnameas before.Safe: if no valid alternative root exists, OTP fails again as
cert_expired, so an expired leaf or intermediate still fails. Partial chains keep working:partial_chainstays, andvalid,valid_peerandextensionevents pass through. Tests added for both.Supersedes #860.