# Task 1.13 — Device authority (Redis allow-list refresher)

**Phase:** 1 — Inbound telemetry
**Status:** ⏸ Paused — deferred until after the real-device pilot test, AND until Directus has a `devices` collection publishing the allow-list to Redis. See ROADMAP.md "Deferred" section. The `DeviceAuthority` seam exists with `AllowAllAuthority` (default, in `src/adapters/teltonika/device-authority.ts`); this task adds `RedisAllowListAuthority`.
**Depends on:** 1.4 (DeviceAuthority seam), 1.10 (metrics)
**Wiki refs:** `docs/wiki/concepts/plane-separation.md`, `docs/wiki/entities/directus.md`, `docs/wiki/entities/redis-streams.md`

## Goal

Provide a real `DeviceAuthority` implementation that classifies an IMEI as `known` or `unknown` by consulting an allow-list **published from Directus into Redis** and cached in-memory in each Ingestion instance. This is the operational link between the business plane (where the source-of-truth `devices` collection lives) and the telemetry plane (where Ingestion makes its handshake decisions).

## Non-goals

- Not a security boundary. Real device security is network-level + downstream filtering. This list is a **soft signal** for observability and (optionally) a hard reject under `STRICT_DEVICE_AUTH`.
- Not a real-time check. The list is cached locally with periodic refresh; new device provisioning takes effect within the refresh interval.

## Deliverables

- `src/adapters/teltonika/redis-allow-list-authority.ts`:
  - `RedisAllowListAuthority` implementing `DeviceAuthority`.
  - In-memory `Set<string>` of allowed IMEIs.
  - Refresh worker that pulls from Redis on a configurable cadence.
  - `start()` runs an initial fetch synchronously (so the cache is warm before the TCP listener accepts) and then starts the periodic refresh.
  - `stop()` halts the refresh ticker.
- `src/main.ts` updated:
  - Read `DEVICE_AUTHORITY_MODE` env var (`allow_all` | `redis_allow_list`, default `allow_all`).
  - Construct the appropriate authority and pass it into the adapter context.
- Documentation in `OPERATIONS.md` (task 1.12) — section "Device authority" describing the env vars, refresh cadence, and Directus contract.

## Specification

### Redis contract

The Ingestion side reads from a single Redis key. Two viable shapes; pick one and stick with it.

**Option 1: Redis Set.** Simple, idiomatic for membership checks.

```
SADD devices:allowed <imei1> <imei2> ...
SMEMBERS devices:allowed       # what the refresher reads
SISMEMBER devices:allowed <imei>   # what an on-demand check would do (we do not use this; we cache)
```

**Option 2: Redis Hash with metadata per device.** Useful if downstream wants more than membership (e.g. device model, firmware version, owner).

```
HSET devices:allowed <imei> '{"model":"FMB920","fw":"03.27"}'
HGETALL devices:allowed
```

**Recommendation: Option 1 (Set).** Membership is the only signal Ingestion uses; metadata belongs in Directus where it's queryable. If a future task needs metadata in Ingestion, switch to Option 2.

### Directus → Redis sync (out of scope for this task)

This task implements the **Ingestion-side reader**. The Directus-side publisher is a separate piece of work in the Directus repo:

- A `devices` collection in Directus with at least `imei`, `active` fields.
- A Directus Flow or hook that, on `items.create | items.update | items.delete` of `devices`, updates the Redis Set:
  - Active inserted/updated → `SADD devices:allowed <imei>`.
  - Deleted or `active=false` → `SREM devices:allowed <imei>`.
- A periodic full-resync (e.g. nightly cron) that snapshots the collection into Redis to recover from any drift: `DEL devices:allowed && SADD devices:allowed <imei1> ... <imeiN>`.

Document this contract in the Ingestion repo's `OPERATIONS.md` so on-call understands the dependency, but the implementation lives in Directus.

### Refresh strategy

```ts
class RedisAllowListAuthority implements DeviceAuthority {
  private cache = new Set<string>();
  private timer?: NodeJS.Timeout;

  constructor(
    private redis: Redis,
    private key: string = 'devices:allowed',
    private intervalMs: number = 30_000,
    private logger: Logger,
    private metrics: Metrics,
  ) {}

  async start(): Promise<void> {
    await this.refresh(); // synchronous initial load before TCP listener is up
    this.timer = setInterval(() => {
      this.refresh().catch((err) => this.logger.warn({ err }, 'allow-list refresh failed'));
    }, this.intervalMs);
  }

  stop(): void { if (this.timer) clearInterval(this.timer); }

  async check(imei: string): Promise<'known' | 'unknown'> {
    return this.cache.has(imei) ? 'known' : 'unknown';
  }

  private async refresh(): Promise<void> {
    const start = process.hrtime.bigint();
    const members = await this.redis.smembers(this.key);
    this.cache = new Set(members);
    const ms = Number(process.hrtime.bigint() - start) / 1e6;
    this.metrics.allowListRefresh.observe(ms / 1000);
    this.metrics.allowListSize.set(this.cache.size);
    this.logger.debug({ size: this.cache.size, took_ms: ms }, 'allow-list refreshed');
  }
}
```

### Failure modes

- **Redis unavailable at startup.** `start()` throws → process exits non-zero → orchestrator restarts. Loud failure, easy to alert. Operators may opt to fall back to `allow_all` via env var change.
- **Redis unavailable mid-flight.** `refresh` fails; the cache stays at last-known-good. `check` keeps working off the stale cache. Log warn; metric for refresh failures. Eventually the cache is "stale forever" if Redis never recovers — that's fine because telemetry is still flowing.
- **Empty allow-list.** A bug or misconfiguration in Directus could publish an empty Set. The Ingestion side will then mark every device as `unknown`. With `STRICT_DEVICE_AUTH=false` (default), this is a visibility problem (alert-worthy) but not a service outage. With `STRICT_DEVICE_AUTH=true`, the entire fleet would be rejected — bad. Add a safety: refuse to apply a refresh result of size 0 unless `ALLOW_EMPTY_ALLOW_LIST=true` is set explicitly. Log error; keep the previous cache.

### Configuration

Add to the env schema (task 1.3):

```ts
DEVICE_AUTHORITY_MODE: z.enum(['allow_all', 'redis_allow_list']).default('allow_all'),
DEVICE_ALLOW_LIST_KEY: z.string().default('devices:allowed'),
DEVICE_ALLOW_LIST_REFRESH_MS: z.coerce.number().int().min(1000).default(30_000),
STRICT_DEVICE_AUTH: z.coerce.boolean().default(false),
ALLOW_EMPTY_ALLOW_LIST: z.coerce.boolean().default(false),
```

### Metrics

Add to task 1.10's inventory:

| Metric | Type | Labels | Description |
|--------|------|--------|-------------|
| `teltonika_allow_list_size` | gauge | — | Number of IMEIs in the local cache. Sudden drops are alert-worthy. |
| `teltonika_allow_list_refresh_duration_seconds` | histogram | — | Time to refresh from Redis. |
| `teltonika_allow_list_refresh_failures_total` | counter | `reason` | Refresh attempts that failed (network, empty-rejected, etc.). |

## Acceptance criteria

- [ ] With `DEVICE_AUTHORITY_MODE=allow_all`, behavior is identical to Phase 1 default — every IMEI is `known`.
- [ ] With `DEVICE_AUTHORITY_MODE=redis_allow_list` and a populated Redis Set, `check(imei)` returns `'known'` for members and `'unknown'` for non-members.
- [ ] Initial load happens before the TCP listener accepts connections.
- [ ] Refresh runs every `DEVICE_ALLOW_LIST_REFRESH_MS` and updates the cache.
- [ ] Empty allow-list refresh is rejected (cache preserved) unless `ALLOW_EMPTY_ALLOW_LIST=true`; metric increments with `reason=empty_rejected`.
- [ ] Mid-flight Redis outage does not crash the service; subsequent successful refresh restores the cache.
- [ ] `teltonika_allow_list_size` and `teltonika_allow_list_refresh_duration_seconds` appear in `/metrics`.
- [ ] `STRICT_DEVICE_AUTH=true` combined with `redis_allow_list` causes `0x00` rejection of unknown IMEIs (verified by integration test).

## Risks / open questions

- **Provisioning lag.** A newly added device waits up to `DEVICE_ALLOW_LIST_REFRESH_MS` before being recognized. Default 30s is fine for most ops; tune down to 5s if the team has a workflow where they provision and immediately expect the device to be `known`.
- **Cache size.** A Set of 100k IMEIs is ~6MB in memory — fine. At 1M+ devices, consider a Bloom filter + Redis fallback for misses, or split into shards. Not a near-term concern.
- **Drift between Directus and Redis.** Hooks-based sync can miss updates if Directus has an issue mid-write. The nightly full-resync cron mitigates. Discussed in the Directus-side task (out of repo scope here).
- **Should `STRICT_DEVICE_AUTH` be observable?** Yes — log at info on startup which mode the authority is in, so operators can verify config without reading env vars.

## Done

(Fill in once complete.)