flex-auth/docs/request-enrichment.md

# Request enrichment

**Published under `FLEX-DEC-2026-012`.** What the evaluator adds to a request
before policy sees it, which value wins where the two disagree, and which digest
a consumer can reproduce.

Nothing here was previously written down. Both defects the decision record covers
were consequences of that: a consumer could not compute the digest it was told to
compute, and a caller could contradict a registry fact and be believed.

## The evaluator overlays registry facts

`POST /v1/check` receives a `CheckRequest`. Before policy evaluates it, the
evaluator resolves the subject and the resource in the registry snapshot and
overlays what it finds:

| Target | Keys the registry contributes |
| --- | --- |
| `subject` | `type`, `tenant`, and attributes `display_name`, `organization_relation`, `roles`, `groups`, plus every subject claim and metadata key |
| `resource` | `type`, and attributes `path`, `parent`, `labels`, `trust_zone`, `owner`, plus every manifest attribute |

Separately, and before either lookup, a non-empty top-level `tenant` propagates
into `subject.tenant` and `resource.tenant` when those are empty.

An unregistered subject or resource is enriched with nothing. `diagnostics`
reports `registry_subject` and `registry_resource` for exactly this reason.

## The registry wins

**A registry fact is an authority statement. The same key on the request is the
caller's proposal about itself.** Where they disagree, the registry's value
reaches policy and the caller's is discarded.

This was the other way round until 2026-09-07, and it made every registry ceiling
and allowlist advisory. Three verified escalations against the shipped
`ops-warden` package, each a single added key on an otherwise-denied request:

| Sent by the caller | Registry says | Was | Now |
| --- | --- | --- | --- |
| `resource.attributes.max_ttl_hours: 99` | `8` | `allow` a 12h certificate | `deny ttl_out_of_bounds` |
| `resource.attributes.allowed_principals: [root, …]` | `[platform, root]` | `allow` | `deny disallowed_principal` |
| `resource.attributes.allowed_subjects: [<caller>]` | `[platform-steward, …]` | `allow` | `deny unknown_subject` |

The third is the one to read twice: a subject the registry does not know
authorized itself by naming itself in the allowlist it was being checked against.

`internal/decision/enrichment_precedence_test.go` asserts the registry value
reaches policy on a request that contradicts it, against attribute keys real
packages branch on — a test over an unused key would pass while the escalation
stayed open.

### Overrides are reported, not silent

`diagnostics.registry_overrode` lists the keys whose caller-supplied value was
displaced, as `subject.<key>` or `resource.<key>`. Empty on an honest request.

A registry that quietly discards a contradicting claim hides that a caller
asserted authority it did not have. The decision is correct either way; the
attempt is worth seeing.

## The residual: keys the registry does not define

**A caller-supplied attribute for a key the registry does not define still
reaches policy.** This is stated rather than fixed.

So a package branching on an attribute its manifest omits is reading caller
input, and a manifest that stops declaring a key silently hands that key to the
caller. Registering the resource is not sufficient — the specific key must be
present in the manifest.

The structural fix is that a policy should be able to tell a registry fact from a
caller assertion at all, which one merged `attributes` map makes impossible.
`FLEX-WP-0025` carries it. Until then, **a policy that enforces a ceiling or an
allowlist MUST read a key its manifest declares**, and that is a review
obligation on every package.

## Which digest a consumer can reproduce

| Field | Over | Consumer-computable |
| --- | --- | --- |
| `binding.request_digest` | the **enriched** request | **No** |
| `binding.submitted_request_digest` | the request **exactly as sent** | **Yes** — this is the §6.4.2 replay test |
| `binding.approval_binding_digest` | the enriched request minus `context.approval` | No, and it does not need to be |

`request_digest` was published as the replay test for consumers. It is not one:
the evaluator hashes the enriched request, the registry is flex-auth's, and a
consumer recomputing over what it sent gets a different value on every request
whose subject or resource the registry knows. `secrets-engine` found this on its
first live request.

**Use `submitted_request_digest` for §6.4 obligation 2.** Nothing is lost.
Enrichment is a function of the request and the registry snapshot, and
`provenance.registry_snapshot_digest` already pins the snapshot — so the
submitted digest together with that digest identifies the evaluated request
completely. Registry staleness between issue and replay is bounded by the
decision's own lifetime and by §9.7.2's per-input-class visibility deadline,
which is the mechanism that already covers it.

`request_digest` keeps its value and meaning: it pins what the decision was
actually a function of, and it is what makes a decision replayable **by
flex-auth** for audit. It is not a consumer check and is now documented as not
being one.

`approval_binding_digest` needs no submitted form. It is compared to
`claim.binding.pdp_digest`, which `approval-engine` recorded from flex-auth's own
output at issue time — a flex-auth value against a flex-auth value, consistent on
both sides. **A consumer must not compute either side of that comparison
itself**; doing so reintroduces exactly this defect on the dual-control path.