--- id: FLEX-WP-0024 type: workplan title: "Sign the decision envelope: the response channel is unauthenticated" domain: infotech repo: flex-auth status: active owner: claude topic_slug: netkingdom planning_priority: P1 planning_order: 240 depends_on_workplans: - FLEX-WP-0021 related_workplans: - FLEX-WP-0019 - FLEX-WP-0023 created: "2026-09-06" updated: "2026-09-06" state_hub_workstream_id: "90577acd-6910-548d-a13e-1dbfdfb8ed27" --- # FLEX-WP-0024 — Sign the decision envelope: the response channel is unauthenticated Opened by `FLEX-DEC-2026-010`, from a question `secrets-engine` asked rather than answering locally: **how is the response channel authenticated?** They declined to choose a transport control for flex-auth's service on the grounds that it is not a consumer's call. Correct, and it is why this is a flex-auth workplan and not a mitigation in their repo. The stance today: pins serve plain HTTP, `flex-auth.decision-record.v1` carries no signature, and a responder that knows the package id and version — both published — can return a well-formed `effect: allow` that passes every check a consumer performs. ## The two things not to get backwards **The digests do not authenticate the responder and cannot.** Every input to them is either sent by the caller or published, so a forger reproduces `request_digest`, `policy_package_digest`, and `registry_snapshot_digest` exactly. Publishing more digests makes a forged envelope look *more* authenticated, not less. **Fail-closed does not cover this.** It protects against a PDP that is absent, not against one that lies. An unreachable PDP denies; a lying PDP allows. ## 1. Publish the stance and stop publishing bare Service names ```task id: FLEX-WP-0024-T01 status: done priority: high state_hub_task_id: "b8fad80d-5c44-5e26-a632-5096e0c0f3c5" ``` Owner: `flex-auth`. **Done 2026-09-06.** `docs/decision-record-contract.md` states that digest recomputation is not responder verification, because the contract is the only document a consumer is guaranteed to read. `docs/operator-caller-access-path.md` carries the reproduced DNS probe and the channel analysis. The trailing-dot FQDN replaced the bare Service name in `examples/secrets-engine/README.md`, `SCOPE.md`, and the `FLEX-WP-0021-T05` handover note — a bare `*.svc.cluster.local` name resolves through `search ad.binect.de` to one unrelated public host, and a name for a service that does not exist resolves to the same address. ## 2. Choose the signature shape and key custody ```task id: FLEX-WP-0024-T02 status: todo priority: high state_hub_task_id: "5482f3cd-36cb-55e0-8c52-0ca2340ed4d7" ``` Owner: `flex-auth`; key custody is **not** ours to invent. - Detached signature over the canonical envelope, preferred over transport-only mTLS for two reasons: it survives the transport, so a decision audited later is still attributable, where mTLS authenticates a connection that no longer exists; and it composes with `FLEX-DEC-2026-009`, since a record that names its authenticated caller *and* carries flex-auth's signature is an audit artifact where either alone is a claim. - Decide the canonical form to sign. The existing canonical-JSON rules from `docs/canonical-request-digest.md` are the obvious basis, but the signed material is the **envelope**, not the request, and it must exclude the signature field itself. Write it down before implementing: an implicit canonicalisation rule is what `FLEX-DEC-2026-007` had to correct. - **Do not mint a key in this repo.** Route custody via `warden route find "decision envelope signing key"` and OpenBao, per the estate credential-routing rule. flex-auth decides the shape; it does not own key material. - State key rotation and how a consumer discovers the current public key, since a consumer that cannot rotate trust has a pinned key that will one day be wrong. Gate: the canonical form, the algorithm, and the custody path are written down and reviewed before any signing code exists. ## 3. Implement signing and verification ```task id: FLEX-WP-0024-T03 status: wait priority: high state_hub_task_id: "041612ea-1be4-5997-8c32-49f8bcc50855" ``` Owner: `flex-auth`. - Add the signature to `schemas/decision_envelope.schema.json` as additive, and state in the contract that `request_digest` is unaffected so no consumer re-pins — the same note that was needed for v2 and for `approval_binding_digest`. - Emit unsigned when no key is configured, and say so in the envelope rather than omitting the field silently. Absence stated, not implied — the `pdp_digest` precedent. - Ship a verification example and a fixture pair in `examples/secrets-engine/replay/`: a genuine signed envelope and one whose payload was altered after signing, so a consumer's verifier is tested against a real failure rather than only a real success. **A verifier that has never seen an invalid signature is untested**, which is the lesson from every fixture suite in `FLEX-DEC-2026-008`. Gate: an altered envelope fails verification, an unaltered one passes, and a consumer can perform both from the fixtures alone. ## 4. Report the gap to gate-house ```task id: FLEX-WP-0024-T04 status: done priority: medium state_hub_task_id: "82d6b75e-e2c6-5e3d-a897-fbdfb7c9094e" ``` Owner: `flex-auth`. §6.4 obligates the PEP to act on a decision and §9.3 splits degraded mode by owner, but **nothing in the standard requires a PDP's response to be authenticable**. So a fully conformant PEP can trust a forged allow while meeting every published obligation. That is a gap in the standard, not only in this implementation, and it belongs in the outstanding v0.8 assent round alongside the `FLEX-DEC-2026-009` finding. ## T04 closed — 2026-09-07 **Done.** Reported as `FLEX-DEC-2026-011` F1, ranked blocking for calling the §6.4 PEP obligations complete and explicitly not blocking anyone's adoption of v0.8 — the condition already exists under v0.7 and is not created by this version. §16 already carries the same observation one layer up, about the standard's own publication path having no digest or freeze discipline; F1 is that observation applied to the artifact the standard regulates.