# Plan: Background New Activity JWT — extended expiry + token pool

**Date:** 2026-03-27 14:29 PST  
**Status:** Draft for implementation  
**Audience:** TimeSafari / crowd-funder developers  
**Related:** `doc/endorser-jwt-background-prefetch-options.md`, `android/.../TimeSafariNativeFetcher.java`, `src/services/notifications/nativeFetcherConfig.ts`, `src/libs/crypto/index.ts`

---

## 1. Problem statement

Background prefetch for New Activity calls Endorser with a Bearer JWT configured via `configureNativeFetcher`. The token previously came from `getHeaders()` → `accessToken()`, which used **`exp` ≈ 60 seconds** (`src/libs/crypto/index.ts`). Prefetch runs **minutes later** in WorkManager **without JavaScript**, so the JWT can be **expired** before the POST (`JWT_VERIFY_FAILED`).

**Goals:**

1. Use JWTs whose **`exp`** covers the gap between **last app-side configure** and **prefetch** (and ideally days without opening the app).
2. Optionally support a **pool** of distinct JWT strings so Endorser can enforce **duplicate-JWT** / **one-time-use** rules without breaking daily prefetch. **Pool size** should follow **`expiryDays + buffer`** (one distinct token per day over the JWT lifetime, plus headroom for retries / edge cases); **implementation uses `BACKGROUND_JWT_POOL_SIZE = 100`** until policy changes.
3. Keep pool size and expiry policy **easy to change** (constants / remote config later).

---

## 2. Guiding principles

| Principle | Implication |
|-----------|-------------|
| **Background has no JS** | Token selection and HTTP must run in **native** (or plugin) code using **persisted** data. |
| **Single source of truth for signing** | Continue using **`createEndorserJwtForDid`** (same keys as today); do not fork crypto in Java/Kotlin. |
| **Configurable pool size** | One constant `BACKGROUND_JWT_POOL_SIZE`; **currently 100**. Size should satisfy **`≥ expiryDays + buffer`** (see below). |
| **Phased delivery** | Ship **extended expiry** first; add **pool** when server duplicate rules require it or in the same release if coordinated. |

### 2.1 Pool size rationale (`expiryDays + buffer`)

For **one New Activity prefetch per day**, each day should use a **distinct** JWT string if the server rejects reuse. Over the JWT lifetime (aligned with **`exp`**), you need at least **one token per day** the pool might be used without regeneration.

**Rule of thumb:**

```text
BACKGROUND_JWT_POOL_SIZE ≥ ceil(BACKGROUND_JWT_EXPIRY_DAYS) + BACKGROUND_JWT_POOL_BUFFER
```

- **`BACKGROUND_JWT_EXPIRY_DAYS`** — human-facing match to `exp` (e.g. **90**); convert to `BACKGROUND_JWT_EXPIRY_SECONDS` for the payload.
- **`BACKGROUND_JWT_POOL_BUFFER`** — extra slots for **same-day retries**, manual tests, or stricter duplicate rules (e.g. **10**).

**Example:** 90‑day `exp` + buffer 10 ⇒ **minimum 100** logical slots. **This plan keeps `BACKGROUND_JWT_POOL_SIZE = 100`** as the shipped default so it matches that example; if `expiryDays` or buffer change later, **bump the constant** so the inequality still holds.

---

## 3. Phases

### Phase A — Extended expiry only (minimum viable)

**Scope**

- Introduce a dedicated mint path for **background / native fetcher** use (name TBD, e.g. `accessTokenForBackgroundNotifications(did)`), producing **one** JWT per configure call with:
  - `iss`: DID (unchanged)
  - `iat`: now
  - `exp`: now + **`BACKGROUND_JWT_EXPIRY_SECONDS`** (derived from **`BACKGROUND_JWT_EXPIRY_DAYS`**; see §2.1 / Phase B constants — **confirm** with Endorser policy)
  - Optional: `jti` or nonce for uniqueness if needed for logging/debug

- **`configureNativeFetcherIfReady`** should pass this token (or keep using a thin wrapper) instead of reusing the **60s** `accessToken()` when configuring native fetcher **only** — **do not** change interactive `getHeaders()` / passkey caching behavior for normal API calls unless product asks for it.

**Files (likely)**

- `src/libs/crypto/index.ts` — new function or parameters; keep `accessToken()` default at 60s for existing callers.
- `src/services/notifications/nativeFetcherConfig.ts` — obtain background JWT via the new mint path, not `getHeaders()`’s generic path, **or** add a dedicated branch that calls the new mint after resolving `did`.

**Native**

- **`TimeSafariNativeFetcher`**: still one `jwtToken` field; no pool yet. Ensure `configure()` is called whenever TS refreshes (startup, resume, Account — already partially covered).

**Exit criteria**

- Logcat: prefetch POST returns **200** (or non-expired 4xx) when user has not opened the app for several **minutes** after configure.
- Endorser accepts **`exp`** far enough in the future (coordinate TTL policy).

---

### Phase B — Token pool (size 100; driven by `expiryDays + buffer`)

**Why**

- Endorser may **reject duplicate JWT strings** (same bearer used twice). One long-lived token could fail on **day 2** if the server marks each JWT as consumed.
- A **pool** of **N** distinct JWTs (different payload, e.g. unique `jti` per token) gives **N** independent strings with the same long **`exp`**. **N** should follow **§2.1** (`expiryDays + buffer`); **100** is the initial **`BACKGROUND_JWT_POOL_SIZE`** (satisfies e.g. 90 + 10).

**Scope**

1. **Constants** (single place, e.g. `src/constants/backgroundJwt.ts` or next to native fetcher config):

   ```text
   BACKGROUND_JWT_EXPIRY_DAYS = 90              // align with Endorser; drives exp
   BACKGROUND_JWT_EXPIRY_SECONDS = 90 * 24 * 60 * 60  // derived
   BACKGROUND_JWT_POOL_BUFFER = 10            // retries / headroom; tune with server team
   BACKGROUND_JWT_POOL_SIZE = 100               // must be >= expiryDays + buffer; adjust if policy changes
   ```

2. **Mint in TS** (uses `createEndorserJwtForDid`):

   - Loop `i = 0 .. POOL_SIZE - 1`
   - Payload: `{ iss, iat, exp, jti: `${did}#bg#${i}` or uuid }` — **confirm** `jti` format with Endorser if required.

3. **Persistence** — native code must read the pool **without JS**:

   - **Option B1 (preferred):** Implement in **`@timesafari/daily-notification-plugin`** (not in the app): extend **`configureNativeFetcher`** to accept an optional JWT pool, persist it for native read. **Handoff spec:** `doc/plugin-feedback-daily-notification-configureNativeFetcher-jwt-pool.md` — copy or reference that file in the plugin repo PR.
   - **Option B2 (app-only, no plugin release):** Write JSON to **Capacitor Preferences** or **encrypted storage** from TS; **TimeSafariNativeFetcher** reads the same store on Android (requires knowing Capacitor’s Android `SharedPreferences` name/key convention or a tiny **bridge** in `MainActivity`). Use only if plugin work is deferred.

4. **Selection policy in `TimeSafariNativeFetcher`** (before each POST):

   - **By calendar day:** `index = (epochDay + offset) % POOL_SIZE` (stable per day).
   - Or **sequential:** persist `lastUsedIndex` in prefs and increment (wrap). **Decision:** document chosen policy; day-based is easier to reason about for “one token per day.”

5. **configureNativeFetcherIfReady** (and any “reset notifications on startup” hook):

   - Regenerate full pool when user opens app (per product decision), then call configure with pool + **current** `apiBaseUrl` / `did`.

6. **iOS:** When iOS native fetcher exists, mirror Android behavior.

**Exit criteria**

- Prefetch succeeds on **consecutive days** with duplicate-JWT enforcement enabled on a **staging** Endorser.
- Pool **refreshes** on startup without breaking dual schedule.

---

## 4. Detailed tasks (checklist)

### Crypto & TypeScript

- [ ] Add `BACKGROUND_JWT_EXPIRY_DAYS`, `BACKGROUND_JWT_EXPIRY_SECONDS`, `BACKGROUND_JWT_POOL_BUFFER`, and `BACKGROUND_JWT_POOL_SIZE` (exported constants), with a **comment** that `POOL_SIZE >= expiryDays + buffer` (see §2.1).
- [ ] Implement `mintBackgroundJwtPool(did: string): Promise<string[]>` (or split single + pool).
- [ ] Ensure each JWT has **unique** `jti` (or equivalent) for duplicate detection.
- [ ] **Do not** break existing `accessToken()` 60s behavior for unrelated features.
- [ ] Wire `configureNativeFetcherIfReady` to pass **single extended token** (Phase A) then **pool** (Phase B).
- [ ] On **logout / identity clear**, clear persisted pool and call plugin clear if needed.

### Android

- [ ] **Phase A:** No structural change if `configure()` still receives one string; verify non-null `jwtToken` after configure.
- [ ] **Phase B:** Parse pool from persisted JSON; implement `selectTokenForRequest()`; use selected token in `Authorization` header instead of sole `jwtToken` field (keep `configure` for `apiBaseUrl` / `did`).
- [ ] Unit or instrumentation tests optional: selection index deterministic.

### Plugin (Option B1 — **daily-notification-plugin** repo)

- [ ] Follow **`doc/plugin-feedback-daily-notification-configureNativeFetcher-jwt-pool.md`** (API shape, Android/iOS, versioning).
- [ ] Release new plugin version; bump dependency in this app.

### Product & server

- [ ] Endorser: confirm **max `exp`**, **duplicate JWT** semantics, recommended **`jti`** format.
- [ ] Document operational limit: if user never opens app for **longer than `exp` allows** (or longer than **pool × daily use** without refresh), prefetch may fail until next open — align with `doc/endorser-jwt-background-prefetch-options.md`.

---

## 5. Security notes

- Longer-lived JWTs and **many** tokens increase impact if device is compromised. Mitigations: **encrypted prefs** where possible, **no logging** of full JWTs, **revocation** story with Endorser (key rotation, deny list).
- Pool regeneration on **login** should replace old pools.

---

## 6. Testing plan

| Test | Expected |
|------|----------|
| Configure → wait **> 5 min** → prefetch | **200** from `plansLastUpdatedBetween` (Phase A) |
| Two consecutive **days** with duplicate-JWT staging | **200** both days (Phase B) |
| Logout | Pool cleared; no stale bearer |
| Lower `BACKGROUND_JWT_POOL_SIZE` in dev only (below `expiryDays + buffer`) | Expect possible reuse / server duplicate errors — use to reproduce failures |

---

## 7. Rollout / staging

1. Implement Phase A behind feature flag **optional** (or direct if low risk).
2. Verify on **test-api.endorser.ch** with server team.
3. Phase B behind flag or same release once server duplicate rules are understood.

---

## 8. Where plugin documentation lives

| Document | Purpose |
|----------|---------|
| **`doc/plan-background-jwt-pool-and-expiry.md`** (this file) | End-to-end app plan: crypto, pool sizing, native host, rollout. |
| **`doc/plugin-feedback-daily-notification-configureNativeFetcher-jwt-pool.md`** | **Plugin-only** handoff: extend `configureNativeFetcher`, persist pool, Android/iOS notes — intended for PRs in **daily-notification-plugin** (or Cursor on that repo). |

Keeping them **separate** avoids mixing consumer app tasks with plugin API contract; the plan **links** to the plugin feedback doc for Option B1.

---

## 9. References

| Topic | Location |
|--------|----------|
| Current 60s `accessToken` | `src/libs/crypto/index.ts` |
| `createEndorserJwtForDid` | `src/libs/endorserServer.ts` |
| Native configure | `src/services/notifications/nativeFetcherConfig.ts` |
| Android HTTP | `android/.../TimeSafariNativeFetcher.java` |
| Options doc (TTL, refresh, BFF) | `doc/endorser-jwt-background-prefetch-options.md` |
| Plugin: `configureNativeFetcher` + JWT pool | `doc/plugin-feedback-daily-notification-configureNativeFetcher-jwt-pool.md` |

---

*Update this plan when Phase A/B ship or when Endorser policy changes.*