approval-engine/docs/caller-authentication.md

Caller authentication

Production accepts only RS256 JWTs verified against KeyCape JWKS with the exact configured issuer and approval-engine audience. exp, iat, sub, principal_type, tenant, roles, scope, and assurance are mandatory. Missing or unverifiable credentials fail closed. The development static-token mode is explicit, file-backed, and refused with --production. The verified tenant must exactly match the service's configured store tenant; cross-tenant reads and mutations are rejected before object lookup.

This check is store isolation, and it is not a statement about the person. It answers "does this caller belong to the store this engine serves", not "is this human a member of the platform zone". GH-DEC-2026-013 rules that a key-cape human tenant claim may be supplied by the client registration rather than asserted by the directory, and forbids a consumer treating the two as equivalent for a decision turning on a fact about the person. Exact string equality cannot see that difference — a string that matches exactly matches whoever asserted it — so the difference is stated here instead.

Consequences this engine accepts deliberately:

• A registration-supplied tenant is admissible for admission to this store. Admission means "arrived through a channel the platform registered", the approver client is static and deployment-owned, and dynamic client registration is excluded from key-cape by design.
• A registration-supplied tenant is not admissible for any doctrine that turns on the approver's own membership — "an approver must be a member of the platform zone" is a fact about the person, and this claim cannot carry it. No such doctrine exists today; if gate-house issues one, it needs a directory-sourced claim and this check does not become that claim by matching.
• When key-cape emits provenance alongside the tenant, this engine records it on the approver entry the way schema v4 records principal_type — an evidence reader should not have to infer provenance from a string that cannot carry it.

Route	Required scope
create approval	approval:create
get approval or claim	approval:read
add approval entry	approval:approve
revoke	approval:revoke
supersede	approval:supersede
consume	approval:consume and service/agent principal
cadence, outbox, storage	approval:observe
explicit heartbeat	approval:emit

Create additionally requires binding.actor == sub. Approval-entry subject, assurance, evidence reference, and principal type are derived from the verified JWT, never the request body.

principal_type is recorded on the entry (schema v4) because subject_id alone cannot answer what kind of principal bound the approval — user:alice is a naming convention, not a verified claim. This engine does not restrict /entries to human principals: whether a service or agent may supply approver evidence is approval doctrine and belongs to gate-house, and the approval-engine-operator registration holds approval:approve today. What this engine owes is that the evidence chain says which it was. Entries written before v4 stay null rather than being back-filled into a claim nobody made. KeyCape owns client registration and scope grants; approval-engine only verifies and enforces them. Requested registrations are:

• audience/resource server approval-engine with the scopes above;
• the secrets-engine PEP service client with approval:read and approval:consume;
• separately governed lifecycle/operator clients with only their needed mutation or observation scopes.

Client credentials belong in OpenBao/operator custody and must not be placed in manifests, logs, State Hub, or this repository.

KeyCape's OpenBao service-auth contract currently emits aud as the OAuth clientId. That pattern must not be reused here. Tokens presented to this API MUST have resource-server audience approval-engine. Requested non-secret client fragments are in docs/keycape-service-registrations.md.