# KeyCape service-auth consumer boundary

secrets-engine now implements the consumer half of KeyCape's accepted
`secrets-engine-openbao` service-auth contract. It performs one explicit HTTPS
`client_credentials` exchange, keeps the resulting JWT in memory, and validates
the non-cryptographic contract before any future OpenBao login:

- subject `service:secrets-engine`, audience/client `secrets-engine-openbao`;
- service principal in `tenant:coulomb`, role `secrets-engine`;
- exact `openbao:login` scope and KeyCape AAL1 client-secret assurance;
- RS256 declaration, bounded issue/expiry timestamps, maximum 15-minute life,
  and renewal when no more than three minutes remain;
- no ID token, refresh token, implicit retry provider, or fallback identity.

The confidential-client secret must be an explicitly selected mode-0600 file
outside every Git worktree. It is sent with HTTP Basic authentication and never
placed in a request body, command argument, evidence record, or object
representation.

This is a scaffold, not a live OpenBao authentication path. JWT payload parsing
does not prove a signature. railiance-platform still owns the exact OpenBao JWT
auth mount/role, issuer keys, claim bindings, token policy, TTL/use limits, and
cryptographic verification. Until that contract is materialized, the provider
is not selected by the CLI and bootstrap/AppRole behavior is not used as an
implicit fallback.

Canonical provider contract:
`key-cape/docs/openbao-service-auth-contract.md` (reviewed 2026-08-23).