fix(googlechat): validate sub claim for Chat issuer tokens to prevent auth bypass

[cubic-dev-ai]

Summary

• Security fix: The Google Chat webhook app-url token verification accepted tokens from any Google Chat app, not just the configured one. When email === CHAT_ISSUER, the function returned { ok: true } immediately without checking the sub claim (Project Number/App ID).
• An attacker could create their own Google Chat app, point its webhook URL at the victim's OpenClaw instance, and have Google sign a valid token with the victim's URL as the aud. The token would pass verification because only aud and email were checked.
• Now requires the sub claim to match the configured appPrincipal for all token types (both standard Chat issuer and Add-on issuer), not only Add-on tokens.
• Renamed param expectedAddOnPrincipal → expectedPrincipal to reflect its broader scope.

Changes

• extensions/googlechat/src/auth.ts — Unified principal validation: check sub claim against expectedPrincipal for both Chat issuer and Add-on issuer tokens before returning ok: true.
• extensions/googlechat/src/monitor-webhook.ts — Updated call sites to use renamed expectedPrincipal param.
• extensions/googlechat/src/targets.test.ts — Added tests for Chat issuer principal validation (match, missing, mismatch); updated existing Add-on tests for renamed param and error messages.
• extensions/googlechat/src/monitor-webhook.test.ts — Updated assertion to use renamed param.

Test plan

• pnpm test -- extensions/googlechat/src/targets.test.ts — 19 tests pass (includes 3 new Chat issuer principal validation tests)
• pnpm test -- extensions/googlechat/src/monitor-webhook.test.ts — 2 tests pass
• pnpm test -- extensions/googlechat/src/monitor.webhook-routing.test.ts — 5 tests pass
• pnpm check — lint/format/type-check all pass

Breaking change note

Deployments using audienceType: "app-url" must now configure appPrincipal (the GCP Project Number) for their Google Chat account. Without it, webhook verification will reject all incoming tokens with "missing principal binding (appPrincipal config required)".

🤖 Generated with Claude Code

[cubic-dev-ai]

No issues found across 4 files

_{Requires human review: This PR modifies core authentication logic to fix a security vulnerability and introduces a breaking change, requiring human oversight to verify the fix and its impact.}