secrets-engine/docs/approval-consumption.md

Approval consumption (PEP)

Status: consumer replay and claim/check/consume join are implemented and exercised against real local components. Live activation requires current PDP contract adoption, client-side and audit admission, and the deployed approval service.

Normative protocol: gate-house/docs/contracts/approval-consumption.md (GH-DEC-2026-003). Implementation surface: approval-engine/docs/approval-consumption.md. This document records how secrets-engine, as the PEP for OpenBao writes, consumes that protocol. It does not redefine it.

Sequence

1. PIP  GET  /v1/approvals/{id}/claim
2. PDP  access-engine Check / decide          → ALLOW
3. PEP  POST /v1/approvals/{id}/consume       → CAS
4. PEP  OpenBao call                          → only after consume succeeds

Each artifact is validated by the layer that owns its data (GH-DEC-2026-005). There is no single bundled object:

Step	Artifact	Owner	Validated by
1	approval-claim	approval-engine	approval_claim.observe_pdp_approval_claim, then decision-time correspondence
2	DecisionEnvelope	flex-auth	authorization.validate_decision_envelope

The claim carries the approval fact: issuer, valid_now, consumption state, binding digest, freshness, reason_code. The envelope carries the decision: effect, exact CheckRequest binding, canonical request digest, lifetime, and the policy package/version pin. Neither republishes the other's data.

ActionAuthorization is deferred and was never ratified (FLEX-DEC-2026-006). It cannot be served from a step-1 call, and nothing here validates it. A ratified post-decision form remains a deferred option.

Replay, approval correspondence and consume identity

FLEX-DEC-2026-012 distinguishes three decision bindings:

Field	Use
submitted_request_digest	Compare to the canonical request actually sent, including the full context.approval claim. Missing or different refuses.
approval_binding_digest	Compare to the claim's issuer-recorded binding.pdp_digest. Both values originate at the evaluator, before and after approval respectively.
request_digest	Preserve the evaluator's enriched request identity for audit and the consume CAS request, alongside its decision id.

The consumer first observes issuer, approval id, validity, freshness, unconsumed state, reason and explicit pdp_path: true with a canonical pdp_digest. resolve_approval_observation returns an observation, never a consume binding. It carries that exact claim into context.approval for the PDP call. Step 2 checks allow, submitted replay identity, policy package/version, decision lifetime and the evaluator-origin approval pair. Claim freshness is rechecked after the call. Only then does authorize_action produce a consume binding.

Registry facts can override caller attributes. The consumer does not duplicate that evaluation or reconstruct the enriched request/approval digest. The native approval digest uses a different vocabulary and is never a fallback. A claim-free decision cannot satisfy the approval join. Changing or removing a claim changes the submitted replay identity even when the approval-free digest stays constant.

Canonical hashing covers tenant, subject, action, resource and nonempty context; request id, policy_version and caring_context are excluded by the producer's contract. Independent producer input/output fixtures verify this boundary.

CAS retry resends the same validated enriched request digest. Fetching a new claim or changing a request is not the same consume operation. Consumption is not backend exactly-once evidence: a response-lost OpenBao operation still needs its own reconciliation before any repeated side effect.

The supported owner loopback forwarding path remains required for PDP transport. A matching digest does not authenticate a malicious responder. Detached signed decisions remain FLEX-WP-0024; this correction grants no new network trust.

The approval-engine object id is never inferred from a State Hub decision UUID. It comes from catalog approval.authorization_id, and is the value in the {id} path segment echoed back as approval_id.

There is no authority constant. The engine previously required provenance.authority == "state-hub", which contradicted its own source: State Hub is a read model and holds no runtime approval authority, so that check failed closed against every correctly issued record. The approval fact's authority is approval-engine (checked as issuer); the decision's is flex-auth.

Every live privileged production handler passes _require_lane_approval, which calls require_production_consume before OpenBaoClient.resolve. Dry-run and plan do not consume. Build/test remain fail-open relative to approval-engine. The three-factor unsafe-demo exception is not a consume path.

Fail closed

Condition	Result
No served consume binding	refuse; no OpenBao
URL/token/authorization id all unset	binding is None → refuse; no OpenBao
Partially configured join (missing subject or policy pin)	raise; never degrade to "unconfigured"
Claim digest, action, or field set mismatch	refuse; no OpenBao
Missing SECRETS_ENGINE_APPROVAL_URL or token file	refuse; no OpenBao
HTTP 409 / different digest	refuse; no OpenBao
Same digest after consume	idempotent success; OpenBao may proceed
401/403/404/503/unreachable	refuse; no OpenBao
Side effect fails after consume	approval is spent; no unconsume

The consume response is mutation evidence (status=consumed plus the presented digest). It is not a permission. Evidence records approval id, digest, idempotence, and consumed-at only. No token, secret, or accessor.

Required configuration

The join is absent by default, so an unconfigured engine behaves exactly as it did before. Production additionally needs:

Variable	Meaning
SECRETS_ENGINE_APPROVAL_URL	approval-engine base URL (claim + consume)
SECRETS_ENGINE_APPROVAL_TOKEN_FILE	explicit bearer credential outside Git; mutually exclusive with the client-secret provider
SECRETS_ENGINE_APPROVAL_CLIENT_SECRET_FILE	protected temporary KeyCape approval-client secret; fresh in-memory token per request (contract)
SECRETS_ENGINE_AUTHORIZATION_SUBJECT_ID / _SUBJECT_TYPE	the acting principal
SECRETS_ENGINE_AUTHORIZATION_POLICY_PACKAGE / _VERSION	the live pin (step 2)
SECRETS_ENGINE_PDP_URL / _PDP_TOKEN_FILE	the per-consumer access-engine pin

The distinct-approver threshold is no longer a consumer-side check. The claim does not expose approver entries; approval-engine folds that requirement into valid_now, which is true only when enough distinct authenticated approvers have been recorded and the object is not consumed, superseded, revoked, or expired.

There is deliberately no default policy pin. The reserved coordinate is secrets-engine.catalog-lane.lifecycle / v1, but that is a reservation, not a publication (FLEX-DEC-2026-005) and must not be configured until FLEX-WP-0021-T02 publishes the package. docs/gated-actions.md supplies the action vocabulary that package is built from.

Step 2 additionally needs the flex-auth-secrets-engine Service DNS. No estate-wide PDP exists by design — flex-auth runs per-consumer cluster-local pins — and that pin has not been created, so the PDP call is not wired yet.

What this does not do

• It does not enable live production. Unreachable-engine stance still fail-closes production until an access-engine decision record is served (SECRETS-WP-0007-T04 / SECRETS-WP-0008-T02).
• It does not render or cache an authorization decision.
• It does not infer consumption from a decision record or from local evidence.