# flex-auth caller identity contract

Status: live A2 proven 2026-08-19 on `flex-auth-user-engine` (`enforce`).

Governing published policy (2026-08-19):

- IAM Profile v0.3 Service Account Flow — audience-scoped, rotating
  workload identity:
  `https://policy.coulomb.social/standards/iam-profile/v0.3/`
- Tenancy Posture v0.1 A2 — inbound caller choke point:
  `https://policy.coulomb.social/standards/tenancy-posture/v0.1/`

user-engine calls `flex-auth-user-engine` with a projected Kubernetes
ServiceAccount token whose audience is exactly `flex-auth`. The adapter reads
the token file for every decision so hourly projection rotation requires no
restart. A missing, empty or unreadable file fails closed as an authorization
denial; the token value is never logged.

flex-auth binds protected system `user-engine` to principal
`system:serviceaccount:user-engine:user-engine`. The token authenticates the
calling workload only. It does not replace the IAM actor/tenant/assurance facts
inside the authorization request and grants no Kubernetes API permission to
user-engine.

Runtime configuration requires `USER_ENGINE_FLEX_AUTH_TOKEN_FILE`. Local
construction keeps the adapter argument optional so unit tests and explicit
non-production adapters remain usable.

The tenant authority seam is distinct: user-engine identifies itself as actor
`user-engine` on tenant lifecycle reads and writes; tenant-engine performs its
own flex-auth decision before store access. Tenant ids remain opaque and are
URL-encoded. No client may infer existence from an unauthorized read.

As of 2026-08-19 `flex-auth-user-engine` is live `enforce` on digest
`sha256:138aa347…` (Helm release rev 4). user-engine `sha256:c501aeb2…`
sends the projected token. The pod security context must set
`runAsUser` / `runAsGroup` / `fsGroup` `10001` (image uid; see
Containerfile). Without `fsGroup`, the projected token is `0440 root:root`
and the adapter never sends `Authorization`. That is persisted in
rapp-user-engine `manifests/runtime.yaml` `e599b4f`. The portal image has
no `curl`; live probes use Python.

## Live promotion probe (USER-WP-0023-T03)

The caller side is deployed: image `sha256:c501aeb2…` (user-engine `7604d31`)
runs in namespace `user-engine` as ServiceAccount `user-engine`, with the
projected token mounted at `/var/run/secrets/flex-auth-caller/token` under
audience `flex-auth` and `USER_ENGINE_FLEX_AUTH_TOKEN_FILE` pointing at it.

Closed 2026-08-19 after `flex-auth-user-engine` flipped to `enforce`.
Do not re-run these against `warn`: step 2 would return a decision.

`POD` is any ready user-engine pod. The portal image has no `curl`; the
recorded run used Python. The bash shape below is the contract, not the
exact live invocation.

```bash
POD=$(kubectl -n user-engine get pod -l app.kubernetes.io/name=user-engine \
  -o jsonpath='{.items[0].metadata.name}')
CHECK=http://flex-auth-user-engine.flex-auth.svc.cluster.local:8080/v1/check
BODY='{"actor":{"issuer":"https://kc.coulomb.social","subject":"probe",
  "tenant":"tenant:friendly:binky","principal_type":"human",
  "audience":["user-engine"],"roles":["tenant-admin"]},
  "resource":{"system":"user-engine","type":"user-engine:user","id":"probe"},
  "action":"user.update","tenant":"tenant:friendly:binky",
  "correlation_id":"probe-t03","context":{}}'
```

1. **A valid caller succeeds.** Expect `200` and a decision id.
   ```bash
   kubectl -n user-engine exec "$POD" -c portal -- sh -c \
     "curl -sS -o /dev/null -w '%{http_code}\n' -X POST $CHECK \
      -H 'Content-Type: application/json' \
      -H \"Authorization: Bearer \$(cat /var/run/secrets/flex-auth-caller/token)\" \
      -d '$BODY'"
   ```
2. **No token is refused.** Expect `401`, not a decision.
   ```bash
   kubectl -n user-engine exec "$POD" -c portal -- sh -c \
     "curl -sS -o /dev/null -w '%{http_code}\n' -X POST $CHECK \
      -H 'Content-Type: application/json' -d '$BODY'"
   ```
3. **user-engine cannot represent another protected system.** Re-run step 1
   with `resource.system` set to `tenant-engine`. Expect a refusal from the
   binding, not an allow: the token binds `user-engine` to
   `system:serviceaccount:user-engine:user-engine` only. That binding is the
   A2 choke point named by Tenancy Posture v0.1; publication does not change
   the remaining operator sequence.

Recorded 2026-08-19 from pod `user-engine-8569d7cb87-fp7px` (flex-auth
message `45852487`):

| Step | Result |
| --- | --- |
| 1. Bearer projected token | `200` `decision:350b46fb42989606` allow `tenant_admin` |
| 2. No Authorization | `401` `unauthenticated` |
| 3. `resource.system=tenant-engine` | `403` `forbidden` |

Digests: flex-auth `sha256:138aa3471c46bca6e814691fa1e6520aedda3dffd743e6b09141ab433afdb64b`,
user-engine `sha256:c501aeb204154d85017565a87fd34cff12e5c48f600d124d3f8c82f11bb9d59c`.
tenant-engine and `policy.enabled` were not moved. A pass on steps 1 and 3
without a 401 on step 2 would have meant enforcement was still off.

## Live cross-service check (USER-WP-0021)

Owed separately to tenant-engine after production served 404 on the lifecycle
routes from 2026-08-13 to 2026-08-16 while our contract-level suite passed
throughout. Contract evidence structurally cannot see a pin rollback, so this
must be exercised live, from a pod, against the real authority.

Use a disposable tenant — never a real one, since retire is a lifecycle
mutation. Through the portal's own platform routes as a platform operator:
`GET` the record, `PATCH` its display name, `retire`, then `reactivate`,
echoing each returned version as the next `If-Match`. Expect `200` throughout
and no `404`, which is what the rollback window produced. Capture the
tenant-engine digest alongside the results; both silent rollbacks this month
were digest-level and neither raised an alert.

This remains owed. It was not run in the 2026-08-19 A2 session.