feat(groom): authenticate agent steps through the local key broker - #290
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Wire key-broker.mjs into all three groom agent jobs (finder, verifier, builder): each starts a loopback key broker right after installing the Claude CLI, then runs the agent with only a dummy ANTHROPIC_API_KEY and ANTHROPIC_BASE_URL pointed at 127.0.0.1:8199. The real model key is no longer present in any step env that invokes `claude` — an agent that dumps its environment leaks only a dummy literal and a loopback URL. The finder/verifier literal-key output scans, which were guarded by the real key being in the agent step env, move to their own `if: always()` steps that hold the key in their own env (they run no agent). The builder's existing patch-capture scan already worked this way and is unchanged. The literal scans are now defence in depth behind the broker. Updates the security-posture comments, the header block, and the groom README to record the broker as the key-exfil close and the scans as backstops.
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📝 WalkthroughWalkthroughThe workflow now uses a loopback API key broker for finder, verifier, and builder agents. Agents receive dummy credentials. Non-agent steps retain the real key and scan finder and verifier outputs. ChangesAPI key isolation
Sequence Diagram(s)sequenceDiagram
participant GroomJob as finder/verifier/builder job
participant Agent as agent step
participant Broker as loopback API key broker
participant API as Anthropic API
GroomJob->>Broker: start broker with real key
GroomJob->>Agent: set dummy key and loopback URL
Agent->>Broker: send API request
Broker->>API: forward request with real key
API-->>Broker: return response
Broker-->>Agent: return response
Priority: ⬇️ Low Merge Risk: 🟡 Moderate · up to An occupied broker port can expose prompts and repository data to an unintended listener. Verify broker ownership before merging. 🚥 Pre-merge checks | ✅ 2✅ Passed checks (2 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
✨ Simplify code
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In @.github/workflows/groom.yml:
- Line 1386: Update the startup loops for the finder, verifier, and builder to
verify the launched key-broker process owns port 8199, rather than treating any
successful TCP connection as readiness. Track the broker PID and require its
process to remain alive plus the broker-specific readiness signal before
proceeding; fail startup if it exits or the signal is absent.
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…s run The finder/verifier/builder key-broker startup loops treated any TCP listener on 127.0.0.1:8199 as readiness. If key-broker.mjs die()s on EADDRINUSE because a pre-existing process already holds the port, the bare TCP probe still connects to that other listener and reports success; the agent step then ships its prompt and repository data to the rogue listener via ANTHROPIC_BASE_URL. Wait for the broker's own bind line in its log and fail fast if the broker PID exits, so readiness means OUR broker owns the port. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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🔍 Cursor Review — Consolidated panel
Triggered by @mattmillerai.
Found 8 finding(s).
| Severity | Count |
|---|---|
| 🟠 High | 1 |
| 🟡 Medium | 1 |
| 🟢 Low | 5 |
| ⚪ Nit | 1 |
Panel: 6/6 reviewers contributed findings.
The 'real key lives ONLY in this step's env' claim was overstated: the same key is also injected into the if: always() leak-scan (finder/verifier) and Capture patch (builder) steps for a literal-value scan. Those steps run no agent, so holding it there adds no exfil surface — but the comment should say so rather than claim the launcher is the only holder. Also note the runners are ephemeral ubuntu-latest (torn down at job end), which is why no explicit broker-stop step is needed. Comment-only; no behavior change. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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main landed #290 (BE-4311, authenticate agent steps through a loopback TCP key-broker) and #291 (BE-4405, extra_denied_paths) while this PR was in review. Resolution: - groom.yml agent/broker/scan regions: kept THIS branch's design (BE-4303 — the full bubblewrap sandbox `agent-sandbox.sh` + UDS `broker.mjs` + in-jail `jail-shim.mjs`, netns no-egress). It structurally SUBSUMES #290's interim TCP key-broker: the jail keeps the real key out of the agent env (as #290 did) AND adds FS confinement + egress isolation. #290's `Start API key broker`, `groom-broker-dummy`/8199 dummy env, and `Lock/Unlock the clone` steps are dropped — the branch comments already note the clone lock + env scrub are subsumed by the jail's read-only clone bind and --clearenv. - #291's `extra_denied_paths`/`EXTRA_DENIED_PATHS` (patch_policy plumbing) and test_patch_policy.py additions: preserved (auto-merged, outside the conflicts). - README: reconciled the stale `key-broker.mjs` "groom.yml wiring (BE-4311)" blockquote to note it was superseded by the sandbox (BE-4303); the asset itself and its tests remain documented. Verified: groom unittest suite 398 passed; shellcheck agent-sandbox.sh + sandbox-tests.sh clean; bash -n on all 45 run: scripts + inner bash -c clean; check_workflow_pins.py OK; check_agents_md.py OK. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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ELI-5
Groom's three AI agents (finder, verifier, builder) used to run with the real Anthropic API key sitting right in their environment. Because a groom agent reads untrusted repo content and can
catfiles, a prompt-injected agent that dumped its whole environment could leak that key. This PR moves the key out: each agent job now starts a tiny loopback proxy (the key broker, already merged) that holds the real key, and the agent runs with only a fake key plus a base-URL pointed at the proxy. If the agent dumps its environment now, all it leaks is the fake stringgroom-broker-dummyandhttp://127.0.0.1:8199.What changed
.github/workflows/groom.yml, in all three agent jobs (audit_find,audit_verify,build):Start API key brokerstep right afterInstall Claude Code. It feeds the real key tokey-broker.mjsover stdin (viaenv -u, never env/argv, so it can't be read back out of/proc/<pid>/{environ,cmdline}), backgrounds it, and waits (up to ~10s) for127.0.0.1:8199to accept a connection before the job proceeds — failing the job loudly if the broker never binds.secrets.ANTHROPIC_API_KEY. It now sets a fixedANTHROPIC_API_KEY: groom-broker-dummy(the CLI requires a non-empty key) plusANTHROPIC_BASE_URL: http://127.0.0.1:8199, so auth flows through the broker, which swaps in the realx-api-keyon the way toapi.anthropic.com.if: always()steps (Scan finder output for leaked key/Scan verifier output for leaked key). They were guarded by[ -n "$ANTHROPIC_API_KEY" ], so with the real key gone from the agent step they would have silently no-op'd; now they run in a step that holds the key in its own env (no agent runs there, so no exfil surface added). The builder's existingCapture patchscan already worked this way and is unchanged.--bareauth note, the "ONLY the model key" env comments, the sandbox security-posture note, and.github/groom/README.md'skey-broker.mjswiring paragraph — record that the broker is the key-exfil close and the literal scans are now defence in depth.Security posture
The key now lives only in the broker-start step's env and the broker process heap. The three
claude-invoking steps (Run finder/verifier/builder) carry no usable credential. If the broker dies mid-run the CLI gets connection-refused and the job fails closed — there is no fallback that puts the key back in the agent env. Widening groom's caller set beyond trusted-default-branch repos still wants a holistic review before flipping.Acceptance grep —
grep -n 'secrets.ANTHROPIC_API_KEY' .github/workflows/groom.ymlnow returns 7 lines: the caller-example comment, the threeStart API key brokersteps, and the three scan steps (finder, verifier, builder patch-capture). Zero are inside a step that invokesclaude. (Theworkflows_callsecret declaration isANTHROPIC_API_KEY:and is retained; it isn't asecrets.reference so it doesn't match the grep.)Provenance
job.workflow_shafalse-positives, the documented BE-4169 carve-out; 0 other findings before or after);python3 -m unittest discover -s .github/groom/tests: 380 passed;check_workflow_pins.py: OK;check_agents_md.py --root .: passed; groom.yml parses as valid YAML.for i in $(seq 1 50), which shellcheck flags SC2034 (the counter is never referenced); changed tofor _ inin all three copies — behaviour is identical. Sandbox comments that mention "the model key in this step's env" as a motivating example were left untouched, per the ticket's instruction that the--bare/ chmod /env -usandbox stays exactly as is (the arbitrary-command-execution threat they guard is unchanged by the broker).Residual
ci-groom.yml(dry-run parity pilot) and confirm the finder completes a normal run through the broker. That is the only end-to-end proof that the pinned CLI 2.1.217 honorsANTHROPIC_BASE_URLand accepts the dummy key against the broker — the unit tests (test_key_broker.py, 380-test suite) prove the proxy's own request handling but not the CLI's base-URL behaviour. A human should run that pilot after merge and confirm the finder resolves turns (not auth-starved / no connection-refused).key-broker.mjs's own author recommends keying the wait on the stdout readiness line (groom-key-broker listening on 127.0.0.1:8199in/tmp/groom-broker.log) instead: a foreign process already holding 8199 would pass a bare connect check while the broker exitsEADDRINUSE. On ephemeral CI runners 8199 is effectively never pre-held, so the risk is low, but matching the readiness line would be a strict hardening worth a follow-up.