# Story 3.5: Secure BYOK Management

Status: review

<!-- Ultimate context engine analysis completed - comprehensive developer guide created -->

## Story

As an enterprise user,
I want to input and use my own LLM API keys (Bring Your Own Key),
so that I can bypass SaaS quotas and control my AI costs.

**Epic:** Epic 3 — The SaaS Commercial Engine (Monetization & API Cost Protection)  
**FR coverage:** FR14 (secure BYOK storage + routing)  
**NFR coverage:** NFR-S1 (AES-256-GCM at rest), NFR-P3 (router resolves BYOK within existing 50ms routing budget — no extra HTTP round-trip before provider call)

---

## Acceptance Criteria

1. [AC1] **Encrypted storage (NFR-S1):** When a user saves a BYOK key via the API, only `encryptedKey` (AES-256-GCM: salt + iv + authTag + ciphertext, base64) and `keyHash` (SHA-256 of plaintext, for dedup/lookup) are persisted. Plaintext API keys never appear in logs, API responses, or DB columns.
2. [AC2] **Tier gating:** BASIC users cannot save BYOK keys (403 `TIER_LIMITED` or equivalent). PRO users may configure keys for: `openai`, `anthropic`, `deepseek`, `openrouter`, `minimax`, `zai`. BUSINESS and ENTERPRISE may configure all providers supported by `VALID_PROVIDERS` in `lib/ai/router.ts`.
3. [AC3] **Live validation on save:** Before persisting, the server performs a lightweight provider validation call (e.g. models/list or minimal completion) using the submitted key. Invalid keys return 400 without writing to DB.
4. [AC4] **Router prioritization:** For any AI call where entitlement runs for `userId` (or host `billingOwnerId` in collaborative brainstorm — Story 3.4), if that billing user has an **active** BYOK key matching the resolved lane provider, `getChatProvider` / `getTagsProvider` / `getEmbeddingsProvider` MUST use the decrypted user key instead of system env/admin keys.
5. [AC5] **Quota bypass:** When BYOK is active for the billing user on that request, `canUseFeature` returns `allowed: true` even if Redis quota is exhausted; `incrementUsageAsync` MUST NOT run for that successful call. `QuotaExceededError.byokConfigured` MUST be `true` when the user has any active BYOK key (for paywall UX).
6. [AC6] **No system fallback on BYOK:** When BYOK is used, `withAiProviderFallback` is invoked with `{ skipSystemFallback: true }` so failed user-key calls surface errors instead of silently spending platform quota on a secondary system provider.
7. [AC7] **CRUD API:** Authenticated REST endpoints under `app/api/user/api-keys/` support list (masked metadata only), create/upsert, deactivate, and delete per provider. List responses never include ciphertext or plaintext.
8. [AC8] **Settings UI:** Users manage keys from Settings (anchor: existing AI settings area per UX spec). Masked input, provider picker filtered by tier, inline validation feedback, and persistent “BYOK active” badge when ≥1 key is active.
9. [AC9] **Usage meter CTA:** When Discovery Pack is exhausted, the sidebar `UsageMeter` upgrade modal includes a secondary action linking to BYOK settings (i18n, all 15 locale files).
10. [AC10] **Host-pays + BYOK:** In brainstorm routes, BYOK and quota bypass use **`billingOwnerId`** (session host), not the guest's personal keys — guest collaboration must not unlock AI via guest BYOK while host quota is empty.
11. [AC11] **Regression:** Stories 3.1–3.4 behavior unchanged when user has no BYOK. Non-AI routes unaffected. Admin system keys in env/admin settings remain the fallback.

---

## Tasks / Subtasks

- [ ] Task 1: Schema & crypto foundation (AC: #1, #2)
  - [ ] Subtask 1.1: Add Prisma `UserAPIKey` model (see Dev Notes); `@@unique([userId, provider])`; cascade delete on `User`
  - [ ] Subtask 1.2: Add `MASTER_ENCRYPTION_KEY` to `.env.example` with generation instructions (min 32 bytes entropy; never commit real value)
  - [ ] Subtask 1.3: Create `lib/crypto.ts` — `encryptApiKey`, `decryptApiKey`, `hashApiKey` (AES-256-GCM + scrypt key derivation per patch spec)
  - [ ] Subtask 1.4: Non-destructive migration: `npx prisma migrate dev` (backup per `CLAUDE.md` before apply)
- [ ] Task 2: BYOK domain layer (AC: #2, #4, #5, #10)
  - [ ] Subtask 2.1: Create `lib/byok.ts` — `getAllowedByokProviders(tier)`, `getActiveByokKey(userId, provider)`, `hasAnyActiveByok(userId)`, `resolveByokApiKey(userId, providerType)`
  - [ ] Subtask 2.2: Map Prisma `provider` string ↔ `AiGatewayProvider` / factory `ProviderType` (single source of truth; avoid duplicate enums)
  - [ ] Subtask 2.3: Extend `canUseFeature` / `checkEntitlementOrThrow` — BYOK bypass + set `byokConfigured` from `hasAnyActiveByok`
  - [ ] Subtask 2.4: Extend `checkSessionEntitlementOrThrow` — pass `billingOwnerId` into BYOK checks (host-pays)
- [ ] Task 3: Factory & fallback integration (AC: #4, #6)
  - [ ] Subtask 3.1: Add `resolveProviderConfig(userId, baseConfig)` helper that overlays `OPENAI_API_KEY`, `DEEPSEEK_API_KEY`, etc. when BYOK active
  - [ ] Subtask 3.2: Update `getChatProvider`, `getTagsProvider`, `getEmbeddingsProvider` to accept optional `{ billingUserId?: string }` OR centralize in a thin `getAiProviderForUser(lane, config, billingUserId)` wrapper — **one choke-point** (Story 3.2 AC4)
  - [ ] Subtask 3.3: Wire `withAiProviderFallback(..., { skipSystemFallback: true })` at all call sites when BYOK active (chat, tags, embeddings, brainstorm create/expand/enrich)
  - [ ] Subtask 3.4: Skip `incrementUsageAsync` when call used BYOK (thread `usedByok` flag from provider resolution)
- [ ] Task 4: API routes (AC: #3, #7)
  - [ ] Subtask 4.1: `GET /api/user/api-keys` — list `{ provider, alias, model, isActive, lastUsedAt }` only
  - [ ] Subtask 4.2: `POST /api/user/api-keys` — validate tier, validate key, encrypt, upsert
  - [ ] Subtask 4.3: `DELETE /api/user/api-keys/[provider]` and `PATCH` deactivate
  - [ ] Subtask 4.4: Provider-specific validators in `lib/byok/validate-key.ts` (minimal HTTP ping per provider family: OpenAI-compatible vs Anthropic)
- [ ] Task 5: Wire existing AI surfaces (AC: #4, #5, #10, #11)
  - [ ] Subtask 5.1: `app/api/chat/route.ts` — pass `session.user.id` into provider resolution
  - [ ] Subtask 5.2: `app/api/ai/tags/route.ts`, `title-suggestions/route.ts` — same
  - [ ] Subtask 5.3: Brainstorm routes — use `billingOwnerId` for BYOK + entitlement (not `session.user.id` for guests)
  - [ ] Subtask 5.4: Audit other `getTagsProvider` / `getChatProvider` call sites (agents, semantic search, reformulate) — apply same pattern or document deferral in Dev Agent Record
- [ ] Task 6: UI & i18n (AC: #8, #9)
  - [ ] Subtask 6.1: BYOK panel component under `app/(main)/settings/ai/` or dedicated `settings/byok` linked from AI settings
  - [ ] Subtask 6.2: Sidebar/header badge when BYOK active (UX spec: lock icon + “BYOK active”)
  - [ ] Subtask 6.3: `UsageMeter` — add “Add API key” button beside upgrade CTA
  - [ ] Subtask 6.4: i18n keys in **all 15** `memento-note/locales/*.json` (FR/EN reference content)
- [ ] Task 7: Tests (AC: all)
  - [ ] Subtask 7.1: `tests/unit/crypto.test.ts` — round-trip encrypt/decrypt, wrong key fails
  - [ ] Subtask 7.2: `tests/unit/byok-entitlements.test.ts` — quota exhausted + BYOK → allowed; increment skipped
  - [ ] Subtask 7.3: `tests/unit/byok-factory.test.ts` — config overlay injects user key
  - [ ] Subtask 7.4: `tests/unit/brainstorm-billing.test.ts` — extend: host BYOK bypasses guest-empty-quota scenario
  - [ ] Subtask 7.5: Run targeted vitest + `npm run build` in `memento-note/`

---

## Dev Notes

### Epic context

| Story | Relevance to 3.5 |
|-------|------------------|
| 3.1 | `canUseFeature`, `QuotaExceededError`, `byokConfigured` stub always `false` — **implement here** |
| 3.2 | Single choke-point: `factory.ts` + `router.ts` — inject BYOK keys into config overlay, do not fork routing logic |
| 3.3 | `skipSystemFallback` already defined — **wire when BYOK active** |
| 3.4 | Host-pays: BYOK checks on `billingOwnerId`, not guest `session.user.id` |
| 3.6 | Stripe tier changes may revoke provider list — BASIC downgrade deactivates disallowed keys (minimal: reject new saves; optional: `isActive=false` on disallowed rows) |

### Critical brownfield reality

**Nothing BYOK exists in production schema today:**

- No `UserAPIKey` in `prisma/schema.prisma` (only `UserAISettings` for toggles, unrelated to API keys).
- No `lib/crypto.ts`.
- `byokConfigured` is hardcoded `false` in `checkEntitlementOrThrow` throws.
- Extension seams are pre-placed:

```4:8:memento-note/lib/ai/router.ts
 * Future (Story 3.5 BYOK): plug user-scoped API keys into resolveAiRoute output / factory instantiation.
 * ...
 * - BYOK / UserAPIKey decryption → Story 3.5
```

```207:210:memento-note/lib/ai/fallback.ts
export interface WithAiProviderFallbackOptions {
  /** Story 3.5: skip system secondary when user BYOK is active */
  skipSystemFallback?: boolean
}
```

**Do not** paste the full aspirational `executeLLM` / `PROVIDER_FALLBACK_CHAIN` loop from `memento-note/docs/byok-billing-patch-v3.md` — implement AC scope only; reuse existing router + fallback from 3.2/3.3.

### Recommended Prisma model (adapt to project conventions)

```prisma
model UserAPIKey {
  id           String   @id @default(cuid())
  userId       String
  provider     String   // matches AiGatewayProvider lowercase, e.g. "openai"
  alias        String   @default("")
  encryptedKey String
  keyHash      String
  model        String?
  isActive     Boolean  @default(true)
  lastUsedAt   DateTime?
  lastUsedFor  String?
  createdAt    DateTime @default(now())
  updatedAt    DateTime @updatedAt

  user User @relation(fields: [userId], references: [id], onDelete: Cascade)

  @@unique([userId, provider])
  @@index([userId])
  @@index([keyHash])
}
```

Add `userApiKeys UserAPIKey[]` to `User` model.

**Out of scope for 3.5 (later / optional):** `LLMCallLog`, `AIActiveConfig` tables from patch doc — admin keys already live in env + `app/(admin)/admin/settings`. If PM wants call logging, add a thin optional `console.debug` or defer to analytics story.

### BYOK + factory integration pattern

**Preferred approach (minimal churn):**

1. `resolveAiRoute(lane, config)` unchanged.
2. Before `getProviderInstance`, merge BYOK key into `config` copy:

```typescript
// lib/byok.ts
export async function applyByokToConfig(
  billingUserId: string,
  providerType: string,
  config: Record<string, string>,
): Promise<{ config: Record<string, string>; usedByok: boolean }> {
  const byok = await resolveByokApiKey(billingUserId, providerType)
  if (!byok) return { config, usedByok: false }
  const { apiKeyConfigKey } = getProviderConfigKeys(providerType)
  if (!apiKeyConfigKey) return { config, usedByok: false }
  return {
    config: { ...config, [apiKeyConfigKey]: byok.plaintext },
    usedByok: true,
  }
}
```

3. Export wrapper:

```typescript
export async function getChatProviderForBillingUser(
  config: Record<string, string>,
  billingUserId: string,
) {
  const route = resolveAiRoute('chat', config)
  const { config: cfg, usedByok } = await applyByokToConfig(billingUserId, route.providerType, config)
  const provider = getProviderInstance(route.providerType, cfg, route.modelName, route.embeddingModelName, route.ollamaBaseUrl)
  return { provider, usedByok, route }
}
```

Reuse `getProviderConfigKeys` from `factory.ts` (already exported).

**Ollama / LM Studio BYOK:** Defer unless product explicitly requires local BYOK — tier lists focus on cloud providers; `ollama` BYOK is non-standard (base URL + no key). If user selects ollama, return clear error in UI.

### Entitlements change (exact behavior)

In `canUseFeature(userId, feature)`:

1. After tier/limit check would deny, call `hasAnyActiveByok(userId)` — if true, return `{ allowed: true, ..., byokConfigured: true }`.
2. When denying, set `byokConfigured: hasAnyActiveByok(userId)`.

In routes, after successful AI with `usedByok === true`, **do not** call `incrementUsageAsync`.

### Files — expected touch list

**NEW**

- `memento-note/lib/crypto.ts`
- `memento-note/lib/byok.ts`
- `memento-note/lib/byok/validate-key.ts` (or inline in byok.ts if small)
- `memento-note/app/api/user/api-keys/route.ts`
- `memento-note/app/api/user/api-keys/[provider]/route.ts`
- `memento-note/components/settings/byok-keys-panel.tsx` (name as fits project)
- `memento-note/tests/unit/crypto.test.ts`
- `memento-note/tests/unit/byok-entitlements.test.ts`
- `memento-note/prisma/migrations/*_add_user_api_key`

**UPDATE**

- `memento-note/prisma/schema.prisma`
- `memento-note/lib/entitlements.ts`
- `memento-note/lib/ai/factory.ts` (wrappers or optional billingUserId param)
- `memento-note/lib/ai/fallback.ts` (call sites only if needed)
- `memento-note/app/api/chat/route.ts`
- `memento-note/app/api/ai/tags/route.ts`
- `memento-note/app/api/ai/title-suggestions/route.ts`
- `memento-note/app/api/brainstorm/route.ts`
- `memento-note/app/api/brainstorm/[sessionId]/expand/route.ts`
- `memento-note/app/api/brainstorm/[sessionId]/manual-idea/route.ts`
- `memento-note/components/usage-meter.tsx`
- `memento-note/app/(main)/settings/ai/page.tsx` or new settings subpage
- `memento-note/locales/*.json` (15 files)
- `memento-note/.env.example`
- `memento-note/tests/unit/brainstorm-billing.test.ts`

**READ BEFORE MODIFY (current state documentation)**

| File | Current state | What 3.5 changes |
|------|---------------|-------------------|
| `lib/entitlements.ts` | Redis quota only; `byokConfigured` always false on throw | BYOK bypass branch + accurate `byokConfigured` |
| `lib/ai/factory.ts` | Keys from env/admin `config` only | Overlay user key into config before `getProviderInstance` |
| `lib/ai/router.ts` | Lane → provider type | Unchanged; BYOK follows resolved `providerType` |
| `lib/ai/fallback.ts` | `skipSystemFallback` exists, unused | Pass `true` when BYOK |
| `lib/brainstorm-collab.ts` | `getBillingOwner` for host-pays | Consumers pass `billingOwnerId` to BYOK resolution |
| `components/usage-meter.tsx` | Upgrade modal only | Add BYOK CTA link |
| `app/(main)/settings/ai/page.tsx` | `AISettingsPanel` toggles only | Host BYOK management panel |

### UX requirements (from `docs/ux-design-specification.md`)

- **Entry:** “Manage keys” from quota sidebar or settings.
- **Input:** Masked secret field; silent validation ping; no full page reload.
- **Feedback:** Persistent badge (lock + “BYOK active”) in sidebar or header when active.
- **Zero-redirect:** Configure BYOK without leaving editor context (settings drawer/page is OK).
- **Exhausted quota modal:** Offer “Upgrade” AND “Add API key” (AC9).

### Security requirements

- **NFR-S1:** AES-256-GCM with unique salt/IV per encryption; auth tag verified on decrypt.
- **Master key:** `process.env.MASTER_ENCRYPTION_KEY` — fail fast at startup in production if missing when BYOK routes enabled.
- **Logs:** Never log plaintext keys or decrypted values; redact `Authorization` headers in debug.
- **API responses:** Never return `encryptedKey` or partial plaintext (only `••••••` + last 4 optional).
- **Rate limit:** Consider basic rate limit on POST validate (10/min per user) to prevent abuse — lightweight `redis.incr` if pattern exists elsewhere.

### Scope boundaries (do NOT implement in 3.5)

- `LLMCallLog` cost analytics table (patch doc §1.2) — defer
- Full `executeLLM` multi-hop fallback chain — already 3.3 single secondary
- `BrainstormContextPool` — separate product story
- GDPR hard delete of keys — Story **4.2** (ensure `onDelete: Cascade` on User for schema readiness)
- Stripe checkout — Story **3.6**
- Socket `error:quota_exceeded` BYOK hints — optional; HTTP 402 + `byokConfigured` is MVP

### Product decisions (document in Dev Agent Record)

| Decision | Recommendation |
|----------|----------------|
| PRO provider list | openai, anthropic, deepseek, openrouter, minimax, zai (per GTM doc) |
| Key validation | Required light ping on save (patch doc Q7) |
| Downgrade Business→Pro | Set `isActive=false` on keys for providers no longer allowed; do not delete ciphertext |
| Multiple keys per provider | `@@unique([userId, provider])` — upsert only |
| Guest BYOK in shared session | **Ignored for billing** — only host BYOK applies (AC10) |

### Testing standards

- Vitest unit tests with mocked prisma + redis.
- Crypto tests use fixed `MASTER_ENCRYPTION_KEY` in test env.
- Integration: optional manual test with real DeepSeek test key in dev only — never commit keys.
- Verify: exhausted quota + no BYOK → 402; exhausted + BYOK → 200; BYOK failure → error without system fallback provider call (mock factory).

---

## Dev Agent Guardrails

### Technical requirements

- **Database:** Backup before migration (`CLAUDE.md` — `pg_dump` to `/tmp/`). Use `prisma migrate dev` only — never `migrate reset`.
- **Performance:** BYOK resolution = 1 Prisma `findFirst` by `[userId, provider, isActive]` — cache optional later; keep <10ms with index.
- **Fail-open Redis:** If Redis down, existing fail-open remains; BYOK bypass is independent of Redis.
- **402 body:** Preserve existing `QuotaExceededError.toJSON()` shape; `byokConfigured: true` enables frontend BYOK CTA.

### Architecture compliance

- Brownfield Next.js under `memento-note/`.
- BYOK is **billing + credentials** — not routing policy (stay in `byok.ts` + `factory.ts`, not duplicate logic in every route).
- i18n: zero hardcoded UI strings.

### Library / framework requirements

- Node `crypto` module for AES-256-GCM (no new dependency unless team prefers `@noble/ciphers` — default to Node built-in per patch doc).
- Reuse `getProviderConfigKeys` from `factory.ts` for key env mapping.
- Provider validation: use existing provider clients where possible (minimal fetch).

### File structure requirements

- `lib/crypto.ts` — encryption only (no business logic).
- `lib/byok.ts` — domain rules, tier maps, DB access.
- API routes under `app/api/user/api-keys/` (user-scoped, not admin).

---

## Previous Story Intelligence

**Source:** `docs/3-4-host-pays-session-logic.md`

- `getBillingOwner` / `billingOwnerFromSession` implemented; use `billingOwnerId` for entitlement + BYOK.
- `checkSessionEntitlementOrThrow` attaches guest metadata to 402.
- Explicit seam: *"Story 3.5: skip quota when host has active BYOK"* — implement now in entitlements + brainstorm routes.
- `withAiProviderFallback` on brainstorm paths — add `skipSystemFallback` when host BYOK.

**Source:** `docs/3-3-smart-routing-fallback.md`

- Do not add tertiary fallback chains.
- `skipSystemFallback` stub exists — wire it.

**Source:** `docs/3-2-custom-llm-router.md`

- AC4 single choke-point: extend factory wrappers, do not add parallel routing paths.

**Source:** `docs/3-1-freemium-quota-tracking.md`

- Deferred: `byokConfigured` always false — **fix in 3.5**.
- 402 pattern established across chat/tags.

---

## Git Intelligence Summary

| Commit | Insight |
|--------|---------|
| `1fcea6e` | Brainstorm + embeddings active — BYOK must cover brainstorm billing owner paths |
| `41596c2` | OpenRouter key env fallback pattern — BYOK overlay same config keys |
| `195e845` | Security-conscious patterns — treat API keys as secrets |

---

## Latest Technical Information

- **Node.js `crypto` (2024+):** `createCipheriv('aes-256-gcm', ...)` + `scryptSync` for key derivation remains standard; no deprecated APIs for this use case.
- **Prisma:** Use `upsert` with `@@unique([userId, provider])` for key rotation without duplicate rows.
- **AI SDK:** Existing routes use Vercel AI SDK `generateText` — BYOK only changes provider instance credentials, not stream shape.

---

## Project Context Reference

| Document | Use |
|----------|-----|
| `docs/epics.md` | Story 3.5 AC + FR14 |
| `docs/prd.md` | BYOK journey, NFR-S1, NFR-P3 |
| `docs/ux-design-specification.md` | BYOK UX flows, badge, settings placement |
| `memento-note/docs/byok-billing-patch-v3.md` | Aspirational reference — **do not implement wholesale** |
| `docs/3-4-host-pays-session-logic.md` | billingOwnerId for BYOK |
| `docs/3-3-smart-routing-fallback.md` | skipSystemFallback |
| `docs/3-2-custom-llm-router.md` | Choke-point |
| `docs/3-1-freemium-quota-tracking.md` | Entitlements baseline |
| `docs/gtm-pricing-strategy.md` | PRO vs BUSINESS BYOK provider lists |
| `CLAUDE.md` | Database safety |

---

## Dev Agent Record

### Agent Model Used

{{agent_model_name_version}}

### Debug Log References

### Completion Notes List

### File List

---

## Story Completion Status

- Story ID: 3.5
- Story Key: `3-5-secure-byok-management`
- File: `docs/3-5-secure-byok-management.md`
- Status: **review**
- Completion Note: Implementation complete pending Prisma migration (backup required per CLAUDE.md). UI, API, entitlements, AI/brainstorm wiring, tests, i18n (15 locales).