Google Cloud Certificate Authority Service integration via REST API
with OAuth2 service account auth (JWT→access token). Synchronous
issuance model, CA pool selection, mutex-guarded token caching,
revocation with RFC 5280 reason mapping. No Google SDK dependency —
all stdlib. 19 tests with httptest mock OAuth2 + CAS API.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
shankar0123