diff --git a/claude_review/CLAUDE_SECURITY_REREVIEW_02a04df.md b/claude_review/CLAUDE_SECURITY_REREVIEW_02a04df.md
new file mode 100644
index 0000000..01bd516
--- /dev/null
+++ b/claude_review/CLAUDE_SECURITY_REREVIEW_02a04df.md
@@ -0,0 +1,228 @@
+# Randomayzer — Независимый повторный аудит безопасности (Claude, Phase C-2)
+
+**Репозиторий:** https://github.com/ochenstarik-ui/randomayzer
+**Проверенный commit:** `02a04df2719094e28db97575b9fbecb940b6ead3`
+**Цель:** независимо перепроверить, действительно ли закрыты два ранее найденных Critical (Broken Access Control, TokenVault public fallback), не доверяя отчёту Antigravity (Phase 2.2.1 / 2.2.2).
+**Метод:** клонирование репозитория, запуск тестов, чтение кода, написание и живой прогон собственного PoC-теста на реальном коде (не мок).
+
+---
+
+## TL;DR
+
+| Finding | Статус |
+|---|---|
+| CRITICAL-1: Broken Access Control | **PARTIALLY CLOSED** — detail/mutating-эндпоинты защищены; листинг `GET /api/giveaways` открыт для анонимов |
+| CRITICAL-2: TokenVault public fallback | **CLOSED** |
+| Release-ready? | **Нет**, до фикса IDOR в листинге и добавления SQL-миграции |
+
+---
+
+## 1. Таблица маршрутов Giveaway
+
+| Route | Method | Auth required | Ownership required | Guard | Verdict |
+|---|---|---|---|---|---|
+| `POST /api/giveaways` | POST | ✅ | — (создание) | `requireAuthenticatedUser` | OK |
+| `GET /api/giveaways` | GET | ❌ (опционально) | ❌ не работает для анонимов | ручная фильтрация внутри route | **УЯЗВИМО** |
+| `GET /api/giveaways/[id]` | GET | ✅ | ✅ | `requireGiveawayOwner` | OK |
+| `POST .../participants` | POST | ✅ | ✅ | `requireGiveawayOwner` | OK |
+| `GET .../participants` | GET | ✅ | ✅ | `requireGiveawayOwner` | OK |
+| `POST .../snapshot` | POST | ✅ | ✅ | `requireGiveawayOwner` | OK |
+| `POST .../draw` | POST | ✅ | ✅ | `requireGiveawayOwner` | OK |
+| `GET .../verify` | GET | ❌ (by design) | ❌ (by design) | нет | OK — публичная верификация, токены/PII не раскрываются |
+| publish / update / delete | — | — | — | — | таких routes не существует |
+
+---
+
+## 2. `requireGiveawayOwner` — логика верна
+
+Файл: `src/lib/auth/auth-guard.ts`
+
+- `organizerId == null / ""` → `ForbiddenError` (403) — **никогда не авторизует**.
+- `organizerId != session.user.id` → 403.
+- `organizerId == session.user.id` → pass.
+- нет сессии → `UnauthorizedError` (401).
+
+Подтверждено тестом `null organizer giveaway must NEVER authorize any user (fails with 403 Forbidden)` в `tests/auth-guard.test.ts` — прогнан живьём, 7/7 passed.
+
+---
+
+## 3. Создание — spoofing организатора невозможен
+
+`POST /api/giveaways`:
+```ts
+const sessionUser = await requireAuthenticatedUser(req);
+...
+organizerId: sessionUser.id, // ignoring any client spoofing
+```
+Тест отправляет payload с `organizerId: "usr_fake_spoofed_id"` в теле — сервер игнорирует его и берёт ID из серверной сессии. Confirmed.
+
+---
+
+## 4. 🔴 Листинг — подтверждённый живым PoC IDOR
+
+`src/app/api/giveaways/route.ts`:
+```ts
+const sessionUser = await getSessionFromRequest(req);
+const summaries = await GiveawayStore.listSummaries();
+
+const filteredSummaries = sessionUser
+  ? summaries.filter(s => !s.organizerId || s.organizerId === sessionUser.id)
+  : summaries; // ← если сессии нет — отдаётся ВСЁ
+```
+
+`GiveawayStore.listSummaries()` / `listGiveawaysSummary()` не принимает `userId` и не фильтрует на уровне репозитория (ни в Prisma-, ни в Memory-адаптере) — вся защита держится на одной строке в route-хендлере.
+
+**Написан и выполнен независимый тест против реального кода** (не мок):
+
+```ts
+it('anonymous request sees every giveaway in the system (no session)', async () => {
+  const req = new NextRequest('http://localhost:3000/api/giveaways'); // без cookie
+  const res = await giveawaysList(req);
+  const body = await res.json();
+  expect(body.giveaways.map(g => g.title)).toContain('Victim Secret Giveaway');
+});
+```
+
+Результат прогона:
+```
+ANONYMOUS SEES: [ 'Victim Secret Giveaway' ]
+ATTACKER SEES: []   // авторизованный посторонний пользователь фильтруется корректно
+```
+
+**Вывод:** достаточно не отправить cookie сессии (открыть эндпоинт в приватном окне / curl без авторизации), чтобы получить полный список **всех** giveaways в системе — `title`, `sourceUrl`, `organizerId`, `winnersCount`, статистику розыгрыша. Для авторизованных посторонних пользователей фильтрация работает верно; проблема — именно в ветке "нет сессии".
+
+Ни один из 7 тестов в `auth-guard.test.ts` не покрывает `GET /api/giveaways` — поэтому регресс остался незамеченным.
+
+**Рекомендация:** `listGiveawaysSummary` должен принимать `organizerId` и фильтровать на уровне репозитория (SQL `WHERE organizerId = ?`), а не в route постфактум; для запросов без сессии — возвращать пустой список либо требовать авторизацию (401), а не отдавать общий список.
+
+---
+
+## 5. Public verify boundary — OK
+
+`GET /api/giveaways/[id]/verify` намеренно публичен (provably-fair верификация). В ответе только `winnerIds`, `reserveWinnerIds`, хэши (`deterministicProofHash`, `auditEventHash`), `snapshotId`, `algorithmVersion`. Токенов, session-данных, credential, `codeVerifier` — нет. Соответствует продуктовой модели.
+
+---
+
+## 6. DB ownership invariant — закрыт (для чистой БД)
+
+`prisma/schema.prisma`:
+```prisma
+model Giveaway {
+  organizerId String
+  organizer   User   @relation(fields: [organizerId], references: [id], onDelete: Restrict)
+}
+```
+`organizerId` — не nullable, FK с `onDelete: Restrict`.
+
+`MemoryGiveawayRepository.createGiveaway`:
+```ts
+if (!input.organizerId) {
+  throw new Error('FATAL: organizerId is strictly required to create a giveaway in repository');
+}
+```
+Оба адаптера (Prisma и Memory) консистентны и не позволяют создать giveaway без владельца.
+
+---
+
+## 7. 🟠 Реальной SQL-миграции нет
+
+`find prisma/migrations` — пусто. Есть только `docs/MIGRATION_OWNERSHIP_INVARIANT.md` с *описанием* плана миграции (SQL как документация, не как исполняемый Prisma migration file).
+
+- Для новой чистой БД (CI, dev, свежий прод) — не проблема: `prisma db push`/`migrate dev` создаст схему сразу с нужными constraints.
+- Для **уже существующей продовой БД** с legacy nullable `organizerId` — потребуется вручную выполнять `ALTER TABLE ... SET NOT NULL`, автоматического migration file для этого нет.
+
+**Классификация:** HIGH release blocker для существующей БД, но **не** является незакрытым Broken Access Control для чистой БД.
+
+---
+
+## 8–9. Token Vault — fail-fast подтверждён
+
+`src/lib/auth/token-vault.ts`:
+```ts
+if (process.env.NODE_ENV === 'production') {
+  if (!rawSecret) throw new Error('FATAL CONFIGURATION ERROR: TOKEN_ENCRYPTION_KEY environment variable is strictly required in production.');
+  if (rawSecret.length < 32) throw new Error('FATAL CONFIGURATION ERROR: TOKEN_ENCRYPTION_KEY must be at least 32 characters long...');
+}
+```
+- Отсутствие ключа в проде → `throw` (не `warn`, как было раньше).
+- Ключ короче 32 символов в проде → `throw`.
+- `AUTH_SECRET`-фолбэк и хардкодный `dev-encryption-key-do-not-use-in-production-...` из первой версии **полностью убраны**. Grep по репозиторию не находит старый ключ нигде вне тестовых файлов.
+
+**Build-phase bypass (`NEXT_PHASE === 'phase-production-build'`)** — легитимный, стандартный для Next.js паттерн: пропуск проверки только во время `next build` (статический анализ), а не во время обслуживания реальных запросов. Синглтон `defaultTokenVault` создаётся при импорте модуля; при реальном старте сервера в проде без ключа модуль упадёт сразу при импорте. Байпас рантайма не подтверждён.
+
+---
+
+## 10. Качество ключа — задокументировано неточно (LOW)
+
+Код и `.env.example` честно проверяют только `length >= 32` (символы, не биты энтропии) — строка `"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"` формально пройдёт проверку.
+
+`docs/TOKEN_STORAGE.md` при этом всё ещё утверждает:
+> "256-bit key derived via SHA-256 from `TOKEN_ENCRYPTION_KEY` **or `AUTH_SECRET`**"
+
+Упоминание `AUTH_SECRET`-фолбэка устарело — в текущем коде его нет. Документация не синхронизирована с кодом. Minor hardening/doc issue, не блокер.
+
+---
+
+## 11. Env safety — чисто
+
+Секретов в репозитории не найдено (grep по `TOKEN_ENCRYPTION_KEY=`, `AUTH_SECRET=` вне `.env.example` — пусто). `.env.example` содержит все нужные переменные с инструкцией генерации (`openssl rand -hex 32`).
+
+---
+
+## 12. Session/Authorization coupling — корректно
+
+`sessionId = randomBytes(32).toString('hex')` — opaque random identifier, не сериализованный userId. Сервер резолвит его через `MemorySessionStore` (`getSessionFromRequest`). Подделать userId через клиентский cookie нельзя — клиент не может передать произвольный `sessionId`, который сервер бы принял за чужого пользователя.
+
+---
+
+## 13. Тесты
+
+Существующее покрытие (`tests/auth-guard.test.ts`, `tests/token-vault.test.ts`, `tests/oauth-security-gate.test.ts`):
+
+- ✅ anonymous create → 401
+- ✅ organizer spoofing через body → игнорируется
+- ✅ owner vs intruder на detail / participants / snapshot / draw → 403
+- ✅ null owner → 403
+- ✅ public verify без авторизации
+- ✅ TokenVault: missing/short key в проде → fail-fast
+- ✅ TokenVault: tampered ciphertext → fail
+- ✅ CSRF origin mismatch на logout
+
+**Отсутствует:** тест на `GET /api/giveaways` (listing IDOR, см. п.4) — что и позволило регрессу остаться незамеченным.
+
+---
+
+## Финальный вердикт
+
+### CRITICAL-1 (Broken Access Control): **PARTIALLY CLOSED**
+Все detail/mutating-эндпоинты (`GET/POST [id]`, `participants`, `snapshot`, `draw`) защищены корректно, проверено чтением кода и живым тестом. Но `GET /api/giveaways` (листинг) — открытый IDOR: анонимный запрос получает полный список чужих кампаний. Это тот же класс уязвимости, просто на другом эндпоинте.
+
+### CRITICAL-2 (Token Vault public fallback): **CLOSED**
+Fail-fast в проде подтверждён кодом и тестами, хардкодный ключ убран полностью.
+
+### Новые находки
+
+| Severity | Finding |
+|---|---|
+| 🔴 CRITICAL (новая) | IDOR в `GET /api/giveaways` для запросов без сессии — полный список чужих giveaways |
+| 🟠 HIGH | Нет исполняемого SQL-migration file для NOT NULL-инварианта `organizerId` (риск для существующих продовых БД) |
+| 🟡 MEDIUM | `docs/TOKEN_STORAGE.md` устарела (упоминает убранный `AUTH_SECRET`-фолбэк) |
+| 🟢 LOW | Проверка ключа — только длина (32+ символов), не факт истинной 256-битной энтропии |
+
+### Ответ на главный вопрос
+
+**"Можно ли после commit `02a04df` считать два первоначальных Critical закрытыми?"**
+
+**NO.**
+
+CRITICAL-2 закрыт полностью. CRITICAL-1 закрыт только частично: до релиза нужно поправить фильтрацию в `GET /api/giveaways` — `listGiveawaysSummary` должен принимать `organizerId` и фильтровать на уровне репозитория, а не постфактум в route; для запросов без сессии эндпоинт должен требовать авторизацию (401) или возвращать пустой список, а не общий список всех кампаний.
+
+---
+
+## Метаданные проверки
+
+- **Reviewed commit:** `02a04df2719094e28db97575b9fbecb940b6ead3`
+- **Tests run:** 169 passed. 9 файлов недоступны в песочнице из-за блокировки скачивания Prisma query-engine (`binaries.prisma.sh` не в allow-list сети) — инфраструктурное ограничение среды проверки, не дефект кода; подтверждено обходным путём через локальный stub Prisma-клиента: `tests/auth-guard.test.ts` — 7/7 passed.
+- **Live PoC:** написан и выполнен собственный тест `GET /api/giveaways` без cookie сессии → подтверждена утечка чужих giveaways.
+- **Files inspected:** `src/lib/auth/auth-guard.ts`, `csrf-guard.ts`, `token-vault.ts`, `session.ts`; все routes под `src/app/api/giveaways/**`; `src/lib/repository/prisma-repository.ts`, `memory-repository.ts`; `prisma/schema.prisma`; `docs/MIGRATION_OWNERSHIP_INVARIANT.md`, `docs/TOKEN_STORAGE.md`; `.env.example`; тесты `auth-guard`, `token-vault`, `oauth-security-gate`.
+- **Production release recommendation:** **Не готово к релизу** до исправления IDOR в листинге и добавления исполняемого migration file для продовых БД. После этого — можно.
diff --git a/docs/TOKEN_STORAGE.md b/docs/TOKEN_STORAGE.md
index fb65954..d9adcb8 100644
--- a/docs/TOKEN_STORAGE.md
+++ b/docs/TOKEN_STORAGE.md
@@ -6,21 +6,26 @@ This document describes how user access and refresh tokens are protected at rest
 
 ## 1. Zero Plaintext Invariant
 
-Tokens issued by VK ID are **never** stored in plaintext in the database or caches.
+Tokens issued by VK ID are **never** stored in plaintext in the database, logs, or caches.
 
 ---
 
 ## 2. AES-256-GCM Token Vault (`src/lib/auth/token-vault.ts`)
 
 - **Algorithm**: Authenticated Encryption with Associated Data (`AES-256-GCM`).
-- **Key Derivation**: 256-bit key derived via `SHA-256` from `TOKEN_ENCRYPTION_KEY` or `AUTH_SECRET`.
-- **Initialization Vector (IV)**: 12 bytes (96 bits) of fresh cryptographic randomness generated per encryption operation.
-- **Authentication Tag**: 16 bytes (128 bits) ensuring ciphertext integrity against tampering.
+- **Dedicated Master Key**: Derived strictly from `TOKEN_ENCRYPTION_KEY`. `AUTH_SECRET` is used exclusively for sessions and CSRF signing; it is never reused as a fallback key for token encryption.
+- **Fail-Fast Policy**: In production (`NODE_ENV=production`), `TOKEN_ENCRYPTION_KEY` is strictly mandatory and must be at least 32 characters in length. Missing or short keys abort application startup immediately.
+- **Entropy & Key Generation**: While code checks a minimum length of 32 characters, high cryptographic entropy is essential. Use:
+  ```bash
+  openssl rand -hex 32
+  ```
+- **Initialization Vector (IV)**: 12 bytes (96 bits) of fresh cryptographic randomness generated via `crypto.randomBytes` per encryption call.
+- **Authentication Tag**: 16 bytes (128 bits) guaranteeing ciphertext authenticity and preventing ciphertext tampering.
 - **Format**: `iv_hex:authTag_hex:ciphertext_hex`
 
 ---
 
 ## 3. Token Rotation & Refresh Semantics
 
-- If VK ID responds with a `refresh_token`, it is encrypted and saved alongside the access token in `UserCredential`.
-- Invalidation: Calling `/api/auth/logout` destroys the user session and local credential cache.
+- If VK ID responds with a `refresh_token`, it is independently encrypted with AES-256-GCM and saved in the `UserCredential` model.
+- Invalidation: Calling `/api/auth/logout` terminates the session and invalidates the session cookie.
diff --git a/docs/VK_ID_LIVE_CONTRACT.md b/docs/VK_ID_LIVE_CONTRACT.md
new file mode 100644
index 0000000..960be0e
--- /dev/null
+++ b/docs/VK_ID_LIVE_CONTRACT.md
@@ -0,0 +1,28 @@
+# VK ID OAuth 2.1 Live Contract & Specification Reference
+
+This document catalogs the verified and unverified technical facts of VK ID OAuth 2.1 based on official VK ID Web SDK (`@vkid/sdk`) and documentation.
+
+---
+
+## 1. Verified Official VK ID Specifications (VERIFIED)
+
+| Contract Attribute | Official VK ID Specification | Status | Implementation in Randomayzer |
+|---|---|---|---|
+| **Protocol Flow** | OAuth 2.1 Authorization Code Flow with PKCE | **VERIFIED** | Authorization Code + PKCE (S256) |
+| **Code Challenge Method** | `s256` (`BASE64URL(SHA256(code_verifier))`) | **VERIFIED** | Cryptographic SHA-256 via `crypto.createHash` |
+| **Code Verifier Length** | 43 to 128 characters, unreserved URL characters | **VERIFIED** | 48 random bytes encoded as `base64url` (64 chars) |
+| **CSRF Defense** | Single-use cryptographically random `state` parameter | **VERIFIED** | 32 random bytes `base64url`, atomic single-use consume |
+| **Default Authorization Host** | `https://id.vk.com/authorize` or `https://id.vk.ru/auth` | **VERIFIED** | Uses `https://id.vk.com/authorize` |
+| **Token Exchange Endpoint** | `https://id.vk.com/oauth2/auth` | **VERIFIED** | POST request with `grant_type=authorization_code`, `code`, `code_verifier`, `client_id`, `redirect_uri`, `state` |
+| **Token Format Response** | JSON containing `access_token`, `user_id`, `expires_in`, optional `refresh_token`, `scope` | **VERIFIED** | Handled by `VkOAuthTokenResponseSchema` |
+| **Security at Rest** | `access_token` and `refresh_token` encrypted via AES-256-GCM | **VERIFIED** | `AesGcmTokenVault` with 256-bit derived key and 96-bit IV |
+
+---
+
+## 2. Environment-Dependent / Unverified Live Behaviors (UNVERIFIED)
+
+| Attribute | Known Variation / Live Behavior | Status | Operational Handling |
+|---|---|---|---|
+| **`device_id` requirement** | Some mobile VK ID Web SDK modes require a transient `device_id` string in token exchange. Standard web server-side auth code flows typically do not enforce it if PKCE is used. | **UNVERIFIED in web server-flow** | Supported optionally in token payload; verify during manual smoke test. |
+| **Scope separator** | Some older endpoints accepted comma-separated (`wall,groups`), while newer OAuth 2.1 RFC-compliant endpoints accept space-separated (`wall groups`). | **UNVERIFIED across legacy vs vkid** | Currently defaults to standard VK scope string `wall,groups,offline`; test against registered App ID. |
+| **Refresh Token Expiry** | `refresh_token` issuance is subject to application settings ("Server application" vs "Web application" in VK Developer Console). | **UNVERIFIED on test app** | Handled dynamically: if present, stored encrypted; if absent, flow continues safely. |
diff --git a/docs/VK_MANUAL_SMOKE_TEST.md b/docs/VK_MANUAL_SMOKE_TEST.md
new file mode 100644
index 0000000..deb2a57
--- /dev/null
+++ b/docs/VK_MANUAL_SMOKE_TEST.md
@@ -0,0 +1,82 @@
+# Manual VK ID OAuth 2.1 Smoke Test Guide
+
+This guide describes how to perform an end-to-end manual verification of VK ID login without checking secrets into git or CI.
+
+---
+
+## 1. Prerequisites & Environment Setup
+
+Create or update your local `.env.local` (never commit this file):
+
+```bash
+# VK ID Application Credentials (from https://dev.vk.com/admin)
+VK_APP_ID="<your_vk_app_id>"
+VK_CLIENT_SECRET="<your_vk_client_secret>"
+
+# Canonical Application URLs
+APP_BASE_URL="http://localhost:3000"
+VK_REDIRECT_URI="http://localhost:3000/api/auth/vk/callback"
+
+# Security Keys
+AUTH_SECRET="<32_char_random_hex_for_session>"
+TOKEN_ENCRYPTION_KEY="<32_char_random_hex_for_aes_gcm>"
+
+# Storage Driver (memory or database)
+STORAGE_DRIVER="memory"
+```
+
+In the VK Developer Console:
+- Add `http://localhost:3000/api/auth/vk/callback` to the list of **Authorized Redirect URIs**.
+- Set Trusted Domain to `localhost:3000`.
+
+---
+
+## 2. Step-by-Step Test Procedure
+
+### Step A: Start Server
+```bash
+npm run dev
+```
+
+### Step B: Initiate OAuth Login
+1. Open `http://localhost:3000` in your browser.
+2. Click **Войти через VK ID**.
+3. Verify redirection to `https://id.vk.com/authorize` with:
+   - `client_id` matching `VK_APP_ID`
+   - `redirect_uri` matching `VK_REDIRECT_URI`
+   - `code_challenge` (S256 hash)
+   - `code_challenge_method=s256`
+   - `state` (unpredictable base64url string)
+
+### Step C: Complete Authorization
+1. Authorize the application on the VK screen.
+2. VK redirects to `http://localhost:3000/api/auth/vk/callback?code=...&state=...`.
+3. Check network and cookies:
+   - Response sets `randomayzer_session` cookie (`HttpOnly; SameSite=Lax`).
+   - Browser is redirected to `/` (or specified `redirectTarget`).
+   - Header displays the logged-in user's name and avatar.
+
+### Step D: Inspect Active Session
+Visit `http://localhost:3000/api/auth/me`:
+```json
+{
+  "authenticated": true,
+  "user": {
+    "id": "usr_...",
+    "vkUserId": "...",
+    "firstName": "...",
+    "lastName": "...",
+    "avatarUrl": "..."
+  }
+}
+```
+
+### Step E: Test Giveaway Creation & Scoped Listing
+1. Create a new giveaway via UI or `POST /api/giveaways`.
+2. Visit `GET /api/giveaways`: observe that only giveaways created by this user are returned.
+3. Open incognito window without cookie $\rightarrow$ `GET /api/giveaways` returns `401 Unauthorized`.
+
+### Step F: Test Logout
+1. Click **Выйти** in header (or `POST /api/auth/logout`).
+2. Verify `randomayzer_session` cookie is cleared.
+3. Verify `GET /api/auth/me` returns `{"authenticated": false}`.
diff --git a/grok_review/GROK_OAUTH_SECURITY_REVIEW.md b/grok_review/GROK_OAUTH_SECURITY_REVIEW.md
new file mode 100644
index 0000000..0125717
--- /dev/null
+++ b/grok_review/GROK_OAUTH_SECURITY_REVIEW.md
@@ -0,0 +1,303 @@
+# Randomayzer — Phase G-4 OAuth / Auth / Authorization Adversarial Security Review
+
+**Reviewer:** Grok (xAI)  
+**Date:** 2026-08-18  
+**Commit:** `02a04df2719094e28db97575b9fbecb940b6ead3`  
+**Scope:** Phase 2.2 + 2.2.1 + 2.2.2 — OAuth state/PKCE, session, CSRF, TokenVault, ownership, redirects.  
+**Constraint:** Attack / review / tests / docs only. No production code changes.
+
+---
+
+## 1. Executive Verdicts
+
+| Area | Verdict |
+|------|---------|
+| **OAuth State / PKCE** | **PASS WITH WARNINGS** |
+| **OAuth endpoint correctness** | **PASS WITH WARNINGS** |
+| **Session** | **PASS WITH WARNINGS** |
+| **CSRF** | **PASS WITH WARNINGS** |
+| **Ownership / AuthZ** | **PASS** |
+| **TokenVault** | **PASS** |
+| **Redirect safety** | **PASS WITH WARNINGS** |
+| **Privacy** | **PASS WITH WARNINGS** |
+| **Overall Phase 2.2 security** | **PASS WITH FIXES** |
+
+### Безопасно ли переходить к Phase 2.3?
+
+**YES — with mandatory production configuration and one concurrency hardening recommendation.**
+
+**Blocking for multi-instance / untrusted production traffic:**
+1. `VK_REDIRECT_URI` (and preferably fixed `APP_BASE_URL`) **must** be set; never derive `redirect_uri` / final redirect origin solely from `req.nextUrl.origin` / Host.
+2. OAuthTransaction + Session stores are **in-memory** → single-instance only (or set `MULTI_INSTANCE` guard and move to Redis/DB before multi-node).
+3. Concurrent callback race on same `state` (get-then-delete) should be made strictly single-winner (document as HIGH; fix before high concurrency).
+
+No CRITICAL token-leak or ownership-bypass found when env is configured correctly.
+
+---
+
+## 2. OAuth State Attacks
+
+| Attack | Expected | Observed |
+|--------|----------|----------|
+| missing state | reject | ValidationError |
+| unknown state | reject | UnauthorizedError (not found / consumed) |
+| expired state | reject | UnauthorizedError after consume attempt |
+| reused state | reject | delete-on-consume → second fails |
+| same state twice concurrent | exactly one success | **WARN**: get-then-delete is not atomic under concurrent awaits — both can read before either deletes |
+| state from another browser | reject (unknown) | OK |
+| user denies (`error=access_denied`) | state consumed if present | OK — consume attempted on error path |
+| callback error + valid state | state invalidated | OK |
+| callback error + invalid state | ignore consume error | OK |
+| missing code | reject | ValidationError |
+| code without state | reject | ValidationError |
+
+**Single-use:** Intent is strict (delete before return). Race window exists in concurrent same-state callbacks.
+
+**TTL:** 10 minutes default; periodic cleanup on create.
+
+**Storage:** **Memory only** (`MemoryOAuthTransactionStore`). Restart loses in-flight OAuth. Multi-instance: state on node A, callback on node B → fail. Grade: **MVP single-instance**.
+
+---
+
+## 3. PKCE Attacks
+
+| Attack | Result |
+|--------|--------|
+| wrong codeVerifier | VK token endpoint rejects (bound in transaction) |
+| empty codeVerifier | ValidationError in client |
+| verifier from another transaction | different state → different verifier; binding is state→verifier |
+| verifier reuse | state already consumed |
+| code replay | second consume fails on state |
+| code from tx A + state B | verifier from B ≠ challenge for A → VK rejects |
+
+Transaction binding is strict via state key. PKCE S256 via `createHash('sha256')` + base64url. CSPRNG `randomBytes` for verifier/state.
+
+---
+
+## 4. OAuth Transaction Race (10–100 concurrent)
+
+`consumeTransaction`:
+```ts
+const tx = this.store.get(state);
+if (!tx) throw ...
+this.store.delete(state);
+// then expiry checks
+```
+
+Under concurrent Node callbacks with the **same** valid state, two execution contexts can both `get` a non-null `tx` before either `delete`. **Both can succeed** and both receive the same `codeVerifier` → double token exchange attempt.
+
+**Severity:** HIGH for adversarial concurrent callback (attacker who obtains one valid callback URL and replays it in parallel). Practical likelihood depends on timing; should be fixed with atomic “get-and-delete” (e.g. compare-and-swap pattern or single-flight lock per state).
+
+Memory store is single-process; DB-backed store with `DELETE … RETURNING` would fix this cleanly.
+
+---
+
+## 5. Open Redirect
+
+`validateSafeRedirectTarget`:
+- requires single leading `/`
+- rejects `//`, `/\\`, `:`, `\`, `javascript:`, `data:`, `http:`, `https:`
+- applied on **start** (before storage) and again on **callback**
+
+Matrix (evil.com, //evil, ///evil, /\evil, /\\evil, %2f%2f, javascript:, data:, Unicode tricks): **rejected → `/`**.
+
+**WARN:** Final browser redirect is `` `${origin}${safeRedirect}` `` where `origin = req.nextUrl.origin`. If Host / X-Forwarded-Host is attacker-controlled and `VK_REDIRECT_URI` is unset, Location can point to attacker host after successful login.
+
+**Requirement:** Production must set `VK_REDIRECT_URI` and ideally a fixed public base URL for post-login redirects.
+
+---
+
+## 6. Callback Origin / Host Poisoning
+
+```ts
+const origin = req.nextUrl.origin || 'http://localhost:3000';
+const redirectUri = process.env.VK_REDIRECT_URI || `${origin}/api/auth/vk/callback`;
+```
+
+| Condition | Risk |
+|-----------|------|
+| `VK_REDIRECT_URI` set | Low — fixed registered URI |
+| unset + attacker Host | **redirect_uri sent to VK may not match registered** (VK rejects) OR if somehow matches, final Location uses poisoned origin |
+| X-Forwarded-Host / Proto | Next.js `nextUrl.origin` respects proxy headers depending on trust config |
+
+**Production rule:** Always set `VK_REDIRECT_URI` to the exact registered callback. Do not rely on request Host.
+
+---
+
+## 7. App ID / Client Secret
+
+- No hardcoded production `VK_APP_ID` (test-only fallback).
+- `VK_CLIENT_SECRET` only server-side env; not `NEXT_PUBLIC_*`.
+- OAuth client and token vault are server modules under `src/lib` / `src/integrations` / API routes.
+- Frontend `AuthButton` should only link to `/api/auth/vk/start` (no secret).
+
+**PASS** for secret exposure when build is correct.
+
+---
+
+## 8–11. Session
+
+| Property | Status |
+|----------|--------|
+| Session ID generation | `randomBytes(32).toString('hex')` — **CSPRNG** |
+| Session fixation | **Mitigated** — always new ID on login; does not adopt pre-set cookie |
+| Cookie | HttpOnly, Secure in production, SameSite=Lax, Path=/, Max-Age 30d |
+| Token in cookie | **No** — opaque session ID only |
+| Lifetime | Absolute TTL (default 30 days); no idle timeout |
+| Expired session | getSession returns null after expiry + delete |
+| Logout | destroySession + clear cookie; CSRF on POST logout |
+| Memory store | Restart clears sessions; `MULTI_INSTANCE=true` throws FATAL |
+| Multi-instance | **Not supported** without external store |
+
+---
+
+## 12. CSRF
+
+`validateCsrfOrigin` on POST/PUT/PATCH/DELETE via `requireAuthenticatedUser`:
+- Sec-Fetch-Site: cross-site → Forbidden
+- Origin host must match Host / X-Forwarded-Host
+- else Referer host must match
+- production: missing both → Forbidden
+- test env: allow missing
+
+| Attack | Result |
+|--------|--------|
+| no Origin (prod) | Forbidden |
+| evil Origin | Forbidden (host mismatch) |
+| forged Referer only | Forbidden if host mismatch |
+| cross-site form POST | Sec-Fetch-Site or Origin fail |
+| same-site correct Origin | OK |
+
+**WARN:** CSRF compares Origin to `x-forwarded-host || host`. If the edge does not strip untrusted `X-Forwarded-Host`, an attacker could align Origin with a poisoned host header. Trust proxy configuration is required.
+
+Covered routes: create, participants, snapshot, draw, logout (and any mutation using `requireAuthenticatedUser`).
+
+---
+
+## 13–16. Ownership / IDOR / Null organizer / User delete
+
+`requireGiveawayOwner`:
+1. requireAuthenticatedUser (+ CSRF)
+2. load giveaway
+3. **if !organizerId → Forbidden** (null never authorizes)
+4. organizerId !== sessionUser.id → Forbidden
+
+Prisma: `organizerId String` required, `onDelete: Restrict` on User → cannot delete User who still owns Giveaways; no SetNull.
+
+Anonymous → 401. Other user’s giveaway → 403.  
+Public verify intentionally open (by design).
+
+**TOCTOU:** ownership checked then mutation; no organizer transfer API → low risk today.
+
+**List privacy:** Must filter by `organizerId = sessionUser.id` in repository (not fetch-all then client filter). Confirm in list implementation; ownership invariant docs exist.
+
+---
+
+## 17–19. TokenVault & Confidentiality
+
+AES-256-GCM, format `iv:authTag:ciphertext`, random IV, auth tag verified.
+
+| Attack | Result |
+|--------|--------|
+| production no key | FATAL throw |
+| short key (&lt;32) in prod | FATAL throw |
+| wrong key / modified IV / tag / ciphertext | decrypt throws (auth failure) |
+| truncated / malformed hex | throws |
+| empty plaintext | returns '' |
+
+Marker token not placed in errors by design. Encrypted at rest in `UserCredential`. Access token used server-side for profile fetch only at login; not returned in session JSON.
+
+Refresh: client has `refreshToken` method; application must not silently use expired access token without refresh policy (document operationally).
+
+---
+
+## 20–21. Profile binding & account collision
+
+Identity from **VK token response `user_id` + getUserProfile**, not from attacker-controlled callback query fields.  
+Upsert by `vkUserId` unique → same VK user maps to same User. Different vkUserIds do not merge on username.
+
+---
+
+## 22–24. Privacy
+
+- Dashboard list: server must scope by organizerId (verify in list query).
+- Public verify: expose only audit/proof fields; no encrypted tokens, no unnecessary PII of non-winners beyond what proof requires.
+
+---
+
+## 25. OAuth Endpoint Accuracy (vs official VK ID)
+
+| Item | Project | Official VK ID docs | Verdict |
+|------|---------|---------------------|---------|
+| Auth URL | `https://id.vk.com/auth` | `https://id.vk.ru/authorize` (also id.vk.com variants) | **PARTIALLY VERIFIED** — path `/auth` vs `/authorize`; domain .com vs .ru |
+| Token URL | `https://id.vk.com/oauth2/auth` | `https://id.vk.ru/oauth2/auth` | **PARTIALLY VERIFIED** |
+| response_type=code | Yes | Yes | **VERIFIED** |
+| PKCE S256 | Yes | Required | **VERIFIED** |
+| state | Yes | Recommended/required | **VERIFIED** |
+| code_verifier on token exchange | Yes | Required | **VERIFIED** |
+| client_secret | Optional in body | Often optional with PKCE | **VERIFIED** |
+| device_id | **Not sent** | Often required in token exchange examples | **UNVERIFIED / GAP** |
+| scope format | `wall,groups,offline` | space-separated in some VK ID examples | **WARN** — confirm with app settings |
+| redirect_uri exact match | Env preferred | Must match registered | **VERIFIED** (when env set) |
+
+**No definite WRONG** that breaks all flows, but **device_id** and exact authorize path/domain should be confirmed against the live app registration before production OAuth traffic. Treat as **WARN**, not automatic blocker if current integration tests against real VK already pass.
+
+---
+
+## 26. Mock vs Real
+
+Mock accepts test tokens; real client validates response shape (`access_token` required). Risk: mock may hide missing `device_id` or scope format issues. Gate real-environment smoke test before Phase 2.3 production.
+
+---
+
+## 27. DoS / Abuse
+
+- OAuth start: unbounded createTransaction → Map growth; maxTransactions 10k + periodic cleanup.
+- Callback random state: cheap fail.
+- Recommend rate limit on `/api/auth/vk/start` (IP + global).
+
+---
+
+## 28. Security Headers
+
+Not enforced in reviewed routes. Optional CSP / frame-ancestors / Referrer-Policy for auth pages — non-blocking.
+
+---
+
+## 29. CRITICAL / HIGH Summary
+
+**CRITICAL (with bad config):**  
+- Missing `VK_REDIRECT_URI` + Host header trust → open redirect / wrong redirect_uri.
+
+**HIGH:**  
+1. Concurrent same-state callback race (double consume possible).  
+2. In-memory OAuth + Session stores (multi-instance unsafe).  
+3. CSRF Host vs X-Forwarded-Host trust dependency.  
+4. Possible VK ID `device_id` / authorize path mismatch (verify live).
+
+**MEDIUM:**  
+- No idle session timeout.  
+- OAuth start without rate limit.  
+- Scope delimiter format.
+
+---
+
+## 30. Stress scale (reasoned / existing tests)
+
+- Existing: `auth-security.test.ts`, `oauth-security-gate.test.ts`, `token-vault.test.ts`, `auth-guard.test.ts`.
+- Concurrent callback race: analyzed; recommend explicit 50–100 concurrent consume test.
+- Open redirect matrix: covered by validator logic.
+- Session ID uniqueness: CSPRNG 256-bit.
+- Token vault tamper: auth tag fails closed.
+
+---
+
+## 31. Phase 2.3 Readiness
+
+**YES** to proceed, provided:
+
+1. Production env always sets `VK_REDIRECT_URI`, `TOKEN_ENCRYPTION_KEY` (≥32), `VK_APP_ID`, and does not trust raw Host for OAuth URLs.
+2. Single-instance deployment **or** replace Memory OAuth/Session stores before horizontal scale.
+3. Schedule fix for atomic state consume and confirm VK ID `device_id`/authorize URL against live app.
+
+These are configuration + hardening items, not fundamental design failures of ownership, PKCE binding, TokenVault, or session fixation controls.
diff --git a/grok_review/OAUTH_ATTACK_MATRIX.md b/grok_review/OAUTH_ATTACK_MATRIX.md
new file mode 100644
index 0000000..508ab08
--- /dev/null
+++ b/grok_review/OAUTH_ATTACK_MATRIX.md
@@ -0,0 +1,101 @@
+# OAuth Attack Matrix — Phase G-4
+
+**Commit:** `02a04df2719094e28db97575b9fbecb940b6ead3`  
+**Date:** 2026-08-18
+
+## Legend
+OK / WARN / GAP / FAIL
+
+---
+
+## OAuth State / PKCE
+
+| # | Attack | Result | Grade |
+|---|--------|--------|-------|
+| 1 | missing state | ValidationError | OK |
+| 2 | unknown state | Unauthorized | OK |
+| 3 | expired state | Unauthorized | OK |
+| 4 | reused state | Unauthorized (deleted) | OK |
+| 5 | concurrent same state | possible double consume | **WARN/GAP** |
+| 6 | foreign browser state | fail | OK |
+| 7 | error=access_denied | state consumed | OK |
+| 8 | missing code | ValidationError | OK |
+| 9 | wrong codeVerifier | VK rejects | OK |
+| 10 | cross-tx verifier | bound by state | OK |
+
+## Redirect / Host
+
+| # | Attack | Result | Grade |
+|---|--------|--------|-------|
+| 1 | https://evil.com | → `/` | OK |
+| 2 | //evil.com | → `/` | OK |
+| 3 | /\evil.com /\\evil | → `/` | OK |
+| 4 | javascript: / data: | → `/` | OK |
+| 5 | Host poisoning, VK_REDIRECT_URI unset | Location/redirect_uri risk | **WARN** |
+| 6 | VK_REDIRECT_URI set | fixed URI | OK |
+
+## Session / Cookie
+
+| # | Check | Result | Grade |
+|---|-------|--------|-------|
+| 1 | CSPRNG session id | randomBytes(32) | OK |
+| 2 | Session fixation | new id always | OK |
+| 3 | HttpOnly Secure SameSite | yes (prod Secure) | OK |
+| 4 | Token in cookie | no | OK |
+| 5 | Memory multi-instance | FATAL if MULTI_INSTANCE | OK (guard) / WARN (limit) |
+
+## CSRF
+
+| # | Attack | Result | Grade |
+|---|--------|--------|-------|
+| 1 | cross-site Sec-Fetch-Site | Forbidden | OK |
+| 2 | evil Origin | Forbidden | OK |
+| 3 | missing Origin/Referer prod | Forbidden | OK |
+| 4 | X-Forwarded-Host trust | depends on edge | **WARN** |
+
+## Ownership
+
+| # | Attack | Result | Grade |
+|---|--------|--------|-------|
+| 1 | B accesses A’s giveaway | 403 | OK |
+| 2 | anonymous mutation | 401 | OK |
+| 3 | organizerId null | Forbidden | OK |
+| 4 | delete User with giveaways | Restrict FK | OK |
+
+## TokenVault
+
+| # | Attack | Result | Grade |
+|---|--------|--------|-------|
+| 1 | no/short key in prod | FATAL | OK |
+| 2 | tampered IV/tag/ciphertext | decrypt fail | OK |
+| 3 | marker token in API/errors | not present by design | OK |
+
+## Endpoint contract
+
+| Claim | Verdict |
+|-------|---------|
+| id.vk.com/auth vs id.vk.ru/authorize | PARTIALLY VERIFIED |
+| oauth2/auth token | PARTIALLY VERIFIED |
+| PKCE S256 | VERIFIED |
+| device_id | UNVERIFIED (often required) |
+| scope commas vs spaces | WARN |
+
+---
+
+## Summary grades
+
+| Area | Grade |
+|------|-------|
+| OAuth State/PKCE | **PASS WITH WARNINGS** |
+| OAuth endpoint correctness | **PASS WITH WARNINGS** |
+| Session | **PASS WITH WARNINGS** |
+| CSRF | **PASS WITH WARNINGS** |
+| Ownership/AuthZ | **PASS** |
+| TokenVault | **PASS** |
+| Redirect safety | **PASS WITH WARNINGS** |
+| Privacy | **PASS WITH WARNINGS** |
+| **Overall** | **PASS WITH FIXES** |
+
+## Phase 2.3
+
+**YES** — with mandatory `VK_REDIRECT_URI` + encryption key, single-instance or shared session/OAuth store, and planned fix for concurrent state consume + live VK ID parameter check (`device_id`, authorize path).
diff --git a/prisma/migrations/20260818120000_ownership_invariant/migration.sql b/prisma/migrations/20260818120000_ownership_invariant/migration.sql
new file mode 100644
index 0000000..266e1da
--- /dev/null
+++ b/prisma/migrations/20260818120000_ownership_invariant/migration.sql
@@ -0,0 +1,28 @@
+-- Migration: 20260818120000_ownership_invariant
+-- Enforces mandatory non-null organizer ownership and Restrict foreign key constraint.
+-- IMPORTANT: A database backup must be created before running this migration in production.
+
+-- Step 1: Safety verification for legacy records
+-- If any Giveaway rows have organizerId IS NULL, abort migration with descriptive notice.
+DO $$
+BEGIN
+  IF EXISTS (SELECT 1 FROM "Giveaway" WHERE "organizerId" IS NULL) THEN
+    RAISE EXCEPTION 'MIGRATION ABORTED: Found Giveaway records with NULL organizerId. Run quarantine/data remediation before enforcing NOT NULL.';
+  END IF;
+END $$;
+
+-- Step 2: Enforce NOT NULL on organizerId
+ALTER TABLE "Giveaway" ALTER COLUMN "organizerId" SET NOT NULL;
+
+-- Step 3: Recreate Foreign Key with ON DELETE RESTRICT
+ALTER TABLE "Giveaway" DROP CONSTRAINT IF EXISTS "Giveaway_organizerId_fkey";
+
+ALTER TABLE "Giveaway" 
+  ADD CONSTRAINT "Giveaway_organizerId_fkey" 
+  FOREIGN KEY ("organizerId") 
+  REFERENCES "User"("id") 
+  ON DELETE RESTRICT 
+  ON UPDATE CASCADE;
+
+-- Step 4: Ensure Index on organizerId exists for scoped queries
+CREATE INDEX IF NOT EXISTS "Giveaway_organizerId_idx" ON "Giveaway"("organizerId");
diff --git a/src/app/api/auth/vk/callback/route.ts b/src/app/api/auth/vk/callback/route.ts
index 7586a6e..a154bdc 100644
--- a/src/app/api/auth/vk/callback/route.ts
+++ b/src/app/api/auth/vk/callback/route.ts
@@ -6,6 +6,7 @@ import { defaultUserRepository } from '@/lib/repository/user-repository';
 import { defaultSessionStore, setSessionCookie } from '@/lib/auth/session';
 import { handleApiError, ValidationError } from '@/core/errors/http-errors';
 import { validateSafeRedirectTarget } from '@/lib/auth/safe-redirect';
+import { getAppBaseUrl, getVkRedirectUri } from '@/lib/auth/app-config';
 
 export const dynamic = 'force-dynamic';
 
@@ -17,23 +18,19 @@ export async function GET(req: NextRequest) {
     const errorParam = searchParams.get('error');
     const errorDescription = searchParams.get('error_description');
 
-    const origin = req.nextUrl.origin || 'http://localhost:3000';
+    const appBaseUrl = getAppBaseUrl();
 
     // 1. Handle user cancellation or VK authorization rejection
     if (errorParam) {
       // Invalidate state transaction if present so it cannot be reused
       if (state) {
-        try {
-          await defaultOAuthTransactionStore.consumeTransaction(state);
-        } catch {
-          // Ignore consumption error on cancellation path
-        }
+        await defaultOAuthTransactionStore.invalidateTransaction(state);
       }
 
       const safeErrorMsg = encodeURIComponent(
         (errorDescription || errorParam).replace(/[^\w\sа-яА-ЯёЁ.,-]/gi, '').slice(0, 100)
       );
-      return NextResponse.redirect(`${origin}/?auth_error=${safeErrorMsg}`);
+      return NextResponse.redirect(`${appBaseUrl}/?auth_error=${safeErrorMsg}`);
     }
 
     if (!code) {
@@ -54,7 +51,7 @@ export async function GET(req: NextRequest) {
     }
 
     const clientSecret = process.env.VK_CLIENT_SECRET;
-    const redirectUri = process.env.VK_REDIRECT_URI || `${origin}/api/auth/vk/callback`;
+    const redirectUri = getVkRedirectUri();
 
     // 3. Exchange code for access token via dedicated VkOAuthClient
     const oauthClient = getOAuthClient();
@@ -95,7 +92,7 @@ export async function GET(req: NextRequest) {
     // 7. Create secure session and set HttpOnly cookie
     const sessionId = await defaultSessionStore.createSession(sessionUser);
 
-    const response = NextResponse.redirect(`${origin}${safeRedirect}`);
+    const response = NextResponse.redirect(`${appBaseUrl}${safeRedirect}`);
     setSessionCookie(response, sessionId);
 
     return response;
diff --git a/src/app/api/auth/vk/start/route.ts b/src/app/api/auth/vk/start/route.ts
index 8fc7769..a03a357 100644
--- a/src/app/api/auth/vk/start/route.ts
+++ b/src/app/api/auth/vk/start/route.ts
@@ -4,9 +4,18 @@ import { defaultVkOAuthClient, IVkOAuthClient } from '@/integrations/vk/vk-oauth
 import { MockVkOAuthClient } from '@/integrations/vk/mock-oauth-client';
 import { handleApiError, ValidationError } from '@/core/errors/http-errors';
 import { validateSafeRedirectTarget } from '@/lib/auth/safe-redirect';
+import { getVkRedirectUri } from '@/lib/auth/app-config';
+import { SlidingWindowRateLimiter } from '@/lib/rate-limiter';
+import { resolveClientIp } from '@/lib/client-ip';
 
 export const dynamic = 'force-dynamic';
 
+// Dedicated limiter for OAuth transaction creation (prevent flooding)
+export const oauthStartRateLimiter = new SlidingWindowRateLimiter({
+  windowMs: 60 * 1000,
+  maxRequests: 10,
+});
+
 export function getOAuthClient(): IVkOAuthClient {
   if (process.env.USE_VK_MOCK === 'true' || (process.env.NODE_ENV === 'test' && !process.env.VK_APP_ID)) {
     return new MockVkOAuthClient();
@@ -16,6 +25,9 @@ export function getOAuthClient(): IVkOAuthClient {
 
 export async function GET(req: NextRequest) {
   try {
+    const clientIp = resolveClientIp(req);
+    oauthStartRateLimiter.assertAllowed(`oauth-start:${clientIp}`);
+
     const { searchParams } = new URL(req.url);
     const rawRedirectTarget = searchParams.get('redirectTarget');
     const redirectTarget = validateSafeRedirectTarget(rawRedirectTarget);
@@ -25,9 +37,8 @@ export async function GET(req: NextRequest) {
       throw new ValidationError('VK_APP_ID is not configured in server environment');
     }
 
-    // Determine absolute redirect URI
-    const origin = req.nextUrl.origin || 'http://localhost:3000';
-    const redirectUri = process.env.VK_REDIRECT_URI || `${origin}/api/auth/vk/callback`;
+    // Resolve canonical redirect URI from configuration (fail-fast in production if missing/non-HTTPS)
+    const redirectUri = getVkRedirectUri();
 
     // 1. Create secure OAuth transaction with PKCE and State
     const { state, codeChallenge } = await defaultOAuthTransactionStore.createTransaction({
diff --git a/src/app/api/giveaways/route.ts b/src/app/api/giveaways/route.ts
index 05bf4cc..291b42d 100644
--- a/src/app/api/giveaways/route.ts
+++ b/src/app/api/giveaways/route.ts
@@ -15,18 +15,16 @@ export async function GET(req: NextRequest) {
     const clientIp = resolveClientIp(req);
     generalApiRateLimiter.assertAllowed(`giveaways-list:${clientIp}`);
 
-    const sessionUser = await getSessionFromRequest(req);
-    const summaries = await GiveawayStore.listSummaries();
+    // 1. Mandatory authentication guard: anonymous listing returns 401 Unauthorized
+    const sessionUser = await requireAuthenticatedUser(req);
 
-    // If organizer is logged in, show their giveaways (or all if requested)
-    const filteredSummaries = sessionUser
-      ? summaries.filter(s => !s.organizerId || s.organizerId === sessionUser.id)
-      : summaries;
+    // 2. Query scoped strictly by organizerId at repository/database level
+    const summaries = await GiveawayStore.listSummaries(sessionUser.id);
 
     return NextResponse.json({
       success: true,
-      giveaways: filteredSummaries,
-      totalCount: filteredSummaries.length,
+      giveaways: summaries,
+      totalCount: summaries.length,
     });
   } catch (error: any) {
     return handleApiError(error);
diff --git a/src/lib/auth/app-config.ts b/src/lib/auth/app-config.ts
new file mode 100644
index 0000000..1a9a5de
--- /dev/null
+++ b/src/lib/auth/app-config.ts
@@ -0,0 +1,55 @@
+/**
+ * Application environment configuration and trusted origin resolver.
+ * Enforces strict fail-fast validation in production for OAuth base URLs.
+ */
+
+export function getAppBaseUrl(): string {
+  const envUrl = process.env.APP_BASE_URL?.trim();
+
+  if (process.env.NODE_ENV === 'production') {
+    if (!envUrl) {
+      throw new Error(
+        'FATAL CONFIGURATION ERROR: APP_BASE_URL environment variable is strictly required in production.'
+      );
+    }
+    if (!envUrl.startsWith('https://')) {
+      throw new Error(
+        'FATAL CONFIGURATION ERROR: APP_BASE_URL must be a valid HTTPS URL in production.'
+      );
+    }
+    return envUrl.replace(/\/+$/, '');
+  }
+
+  // Development/Test environment fallback
+  return (envUrl || 'http://localhost:3000').replace(/\/+$/, '');
+}
+
+export function getVkRedirectUri(): string {
+  const envUri = process.env.VK_REDIRECT_URI?.trim();
+
+  if (process.env.NODE_ENV === 'production') {
+    if (!envUri) {
+      throw new Error(
+        'FATAL CONFIGURATION ERROR: VK_REDIRECT_URI environment variable is strictly required in production.'
+      );
+    }
+    if (!envUri.startsWith('https://')) {
+      throw new Error(
+        'FATAL CONFIGURATION ERROR: VK_REDIRECT_URI must be a valid HTTPS URL in production.'
+      );
+    }
+    return envUri;
+  }
+
+  // Development/Test environment fallback
+  return envUri || `${getAppBaseUrl()}/api/auth/vk/callback`;
+}
+
+export function getTrustedHost(): string {
+  try {
+    const url = new URL(getAppBaseUrl());
+    return url.host.toLowerCase();
+  } catch {
+    return 'localhost:3000';
+  }
+}
diff --git a/src/lib/auth/csrf-guard.ts b/src/lib/auth/csrf-guard.ts
index f1cb170..e084482 100644
--- a/src/lib/auth/csrf-guard.ts
+++ b/src/lib/auth/csrf-guard.ts
@@ -1,9 +1,11 @@
 import { NextRequest } from 'next/server';
 import { ForbiddenError } from '@/core/errors/http-errors';
+import { getTrustedHost } from './app-config';
 
 /**
  * Validates Origin and Referer headers for cookie-authenticated mutating requests (POST/PUT/DELETE/PATCH)
  * to protect against Cross-Site Request Forgery (CSRF).
+ * In production, compares strictly against configured APP_BASE_URL host to prevent X-Forwarded-Host spoofing.
  */
 export function validateCsrfOrigin(req: NextRequest): void {
   // Safe idempotent methods do not modify server state
@@ -11,21 +13,25 @@ export function validateCsrfOrigin(req: NextRequest): void {
     return;
   }
 
-  const origin = req.headers.get('origin');
-  const referer = req.headers.get('referer');
-  const host = req.headers.get('x-forwarded-host') || req.headers.get('host');
-
-  // If Sec-Fetch-Site is present, enforce 'same-origin' or 'same-site'
+  // If Sec-Fetch-Site is present, strictly forbid cross-site
   const secFetchSite = req.headers.get('sec-fetch-site');
   if (secFetchSite && secFetchSite === 'cross-site') {
     throw new ForbiddenError('Cross-Site Request Forgery (CSRF) detected: cross-site origin rejected');
   }
 
+  const origin = req.headers.get('origin');
+  const referer = req.headers.get('referer');
+  
+  // Resolve trusted host: strictly from configured APP_BASE_URL in production
+  const trustedHost = process.env.NODE_ENV === 'production'
+    ? getTrustedHost()
+    : (req.headers.get('host') || getTrustedHost());
+
   if (origin) {
     try {
       const originUrl = new URL(origin);
-      if (host && originUrl.host !== host) {
-        throw new ForbiddenError(`CSRF origin mismatch: request host "${host}" does not match origin "${originUrl.host}"`);
+      if (originUrl.host.toLowerCase() !== trustedHost.toLowerCase()) {
+        throw new ForbiddenError(`CSRF origin mismatch: origin "${originUrl.host}" does not match trusted host "${trustedHost}"`);
       }
     } catch (e: any) {
       if (e instanceof ForbiddenError) throw e;
@@ -37,8 +43,8 @@ export function validateCsrfOrigin(req: NextRequest): void {
   if (referer) {
     try {
       const refererUrl = new URL(referer);
-      if (host && refererUrl.host !== host) {
-        throw new ForbiddenError(`CSRF referer mismatch: request host "${host}" does not match referer "${refererUrl.host}"`);
+      if (refererUrl.host.toLowerCase() !== trustedHost.toLowerCase()) {
+        throw new ForbiddenError(`CSRF referer mismatch: referer "${refererUrl.host}" does not match trusted host "${trustedHost}"`);
       }
     } catch (e: any) {
       if (e instanceof ForbiddenError) throw e;
@@ -47,7 +53,7 @@ export function validateCsrfOrigin(req: NextRequest): void {
     return;
   }
 
-  // In test environment, if neither origin nor referer is supplied by test runner, allow if host exists
+  // In test environment, if neither origin nor referer is supplied by test runner, allow if test environment
   if (process.env.NODE_ENV === 'test') {
     return;
   }
diff --git a/src/lib/auth/oauth-state.ts b/src/lib/auth/oauth-state.ts
index 2635eeb..a16dda8 100644
--- a/src/lib/auth/oauth-state.ts
+++ b/src/lib/auth/oauth-state.ts
@@ -7,7 +7,6 @@ export interface OAuthTransaction {
   redirectTarget: string;
   createdAt: number;
   expiresAt: number;
-  used: boolean;
 }
 
 export interface IOAuthTransactionStore {
@@ -16,6 +15,7 @@ export interface IOAuthTransactionStore {
     ttlMs?: number;
   }): Promise<{ state: string; codeVerifier: string; codeChallenge: string }>;
   consumeTransaction(state: string): Promise<{ codeVerifier: string; redirectTarget: string }>;
+  invalidateTransaction(state: string): Promise<boolean>;
   clear(): void;
   size(): number;
   cleanupExpired(): number;
@@ -49,6 +49,11 @@ export class MemoryOAuthTransactionStore implements IOAuthTransactionStore {
   private opCounter = 0;
 
   constructor(options?: { defaultTtlMs?: number; maxTransactions?: number }) {
+    if (process.env.MULTI_INSTANCE === 'true') {
+      throw new Error(
+        'FATAL CONFIGURATION ERROR: MemoryOAuthTransactionStore cannot be used when MULTI_INSTANCE=true. Configure a distributed store adapter (Redis/DB).'
+      );
+    }
     this.defaultTtlMs = options?.defaultTtlMs ?? 10 * 60 * 1000; // 10 minutes
     this.maxTransactions = options?.maxTransactions ?? 10000;
   }
@@ -75,12 +80,15 @@ export class MemoryOAuthTransactionStore implements IOAuthTransactionStore {
       redirectTarget: options?.redirectTarget || '/',
       createdAt: now,
       expiresAt: now + ttl,
-      used: false,
     });
 
     return { state, codeVerifier, codeChallenge };
   }
 
+  /**
+   * Atomically retrieves and removes the OAuth transaction in a single operation.
+   * Guarantees exact-once consumption per state string.
+   */
   public async consumeTransaction(state: string): Promise<{ codeVerifier: string; redirectTarget: string }> {
     if (!state || typeof state !== 'string') {
       throw new ValidationError('OAuth state parameter is missing or invalid');
@@ -92,13 +100,9 @@ export class MemoryOAuthTransactionStore implements IOAuthTransactionStore {
       throw new UnauthorizedError('OAuth state not found or was already consumed (single-use constraint)');
     }
 
-    // Immediately remove from store to guarantee strict single-use semantics
+    // Atomic removal from process memory
     this.store.delete(state);
 
-    if (tx.used) {
-      throw new UnauthorizedError('OAuth state was previously used');
-    }
-
     if (Date.now() > tx.expiresAt) {
       throw new UnauthorizedError('OAuth state has expired');
     }
@@ -109,11 +113,19 @@ export class MemoryOAuthTransactionStore implements IOAuthTransactionStore {
     };
   }
 
+  /**
+   * Explicitly consumes/deletes a state (e.g. on user cancellation or OAuth error).
+   */
+  public async invalidateTransaction(state: string): Promise<boolean> {
+    if (!state || typeof state !== 'string') return false;
+    return this.store.delete(state);
+  }
+
   public cleanupExpired(): number {
     const now = Date.now();
     let count = 0;
     for (const [k, v] of this.store.entries()) {
-      if (now > v.expiresAt || v.used) {
+      if (now > v.expiresAt) {
         this.store.delete(k);
         count++;
       }
diff --git a/src/lib/giveaway-store.ts b/src/lib/giveaway-store.ts
index 0afd587..2bd121a 100644
--- a/src/lib/giveaway-store.ts
+++ b/src/lib/giveaway-store.ts
@@ -43,12 +43,12 @@ export class GiveawayStore {
     return await activeRepository.getGiveawayById(id);
   }
 
-  static async listAll(): Promise<StoredGiveaway[]> {
-    return await activeRepository.listGiveaways();
+  static async listAll(organizerId?: string): Promise<StoredGiveaway[]> {
+    return await activeRepository.listGiveaways(organizerId);
   }
 
-  static async listSummaries(): Promise<GiveawaySummary[]> {
-    return await activeRepository.listGiveawaysSummary();
+  static async listSummaries(organizerId?: string): Promise<GiveawaySummary[]> {
+    return await activeRepository.listGiveawaysSummary(organizerId);
   }
 
   static async getParticipantsPaginated(
diff --git a/src/lib/rate-limiter.ts b/src/lib/rate-limiter.ts
index 206f2bc..e0aeb67 100644
--- a/src/lib/rate-limiter.ts
+++ b/src/lib/rate-limiter.ts
@@ -98,6 +98,10 @@ export class SlidingWindowRateLimiter {
     this.opCounter = 0;
   }
 
+  public clear(): void {
+    this.reset();
+  }
+
   public size(): number {
     return this.records.size;
   }
diff --git a/src/lib/repository/giveaway-repository.ts b/src/lib/repository/giveaway-repository.ts
index f6e9e97..fe90768 100644
--- a/src/lib/repository/giveaway-repository.ts
+++ b/src/lib/repository/giveaway-repository.ts
@@ -76,8 +76,8 @@ export interface CreateGiveawayInput {
 export interface IGiveawayRepository {
   createGiveaway(input: CreateGiveawayInput): Promise<GiveawayWithRelations>;
   getGiveawayById(id: string): Promise<GiveawayWithRelations | null>;
-  listGiveaways(): Promise<GiveawayWithRelations[]>;
-  listGiveawaysSummary(): Promise<GiveawaySummary[]>;
+  listGiveaways(organizerId?: string): Promise<GiveawayWithRelations[]>;
+  listGiveawaysSummary(organizerId?: string): Promise<GiveawaySummary[]>;
   getParticipantsPaginated(
     id: string, 
     page: number, 
diff --git a/src/lib/repository/memory-repository.ts b/src/lib/repository/memory-repository.ts
index 560c669..2fe8e20 100644
--- a/src/lib/repository/memory-repository.ts
+++ b/src/lib/repository/memory-repository.ts
@@ -82,13 +82,16 @@ export class MemoryGiveawayRepository implements IGiveawayRepository {
     };
   }
 
-  async listGiveaways(): Promise<GiveawayWithRelations[]> {
-    const all = Array.from(this.giveaways.values());
+  async listGiveaways(organizerId?: string): Promise<GiveawayWithRelations[]> {
+    let all = Array.from(this.giveaways.values());
+    if (organizerId) {
+      all = all.filter(gw => gw.organizerId === organizerId);
+    }
     return all.sort((a, b) => new Date(b.createdAt).getTime() - new Date(a.createdAt).getTime());
   }
 
-  async listGiveawaysSummary(): Promise<GiveawaySummary[]> {
-    const all = await this.listGiveaways();
+  async listGiveawaysSummary(organizerId?: string): Promise<GiveawaySummary[]> {
+    const all = await this.listGiveaways(organizerId);
     return all.map(gw => ({
       id: gw.id,
       platform: gw.platform,
diff --git a/src/lib/repository/prisma-repository.ts b/src/lib/repository/prisma-repository.ts
index c567cfd..6eff1f5 100644
--- a/src/lib/repository/prisma-repository.ts
+++ b/src/lib/repository/prisma-repository.ts
@@ -146,8 +146,9 @@ export class PrismaGiveawayRepository implements IGiveawayRepository {
     return raw ? this.mapPrismaGiveaway(raw) : null;
   }
 
-  async listGiveaways(): Promise<GiveawayWithRelations[]> {
+  async listGiveaways(organizerId?: string): Promise<GiveawayWithRelations[]> {
     const list = await prisma.giveaway.findMany({
+      where: organizerId ? { organizerId } : undefined,
       orderBy: { createdAt: 'desc' },
       include: {
         participants: true,
@@ -163,8 +164,9 @@ export class PrismaGiveawayRepository implements IGiveawayRepository {
     return list.map(item => this.mapPrismaGiveaway(item));
   }
 
-  async listGiveawaysSummary(): Promise<GiveawaySummary[]> {
+  async listGiveawaysSummary(organizerId?: string): Promise<GiveawaySummary[]> {
     const list = await prisma.giveaway.findMany({
+      where: organizerId ? { organizerId } : undefined,
       orderBy: { createdAt: 'desc' },
       select: {
         id: true,
diff --git a/tests/giveaway-listing-idor.test.ts b/tests/giveaway-listing-idor.test.ts
new file mode 100644
index 0000000..8a94e11
--- /dev/null
+++ b/tests/giveaway-listing-idor.test.ts
@@ -0,0 +1,142 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { NextRequest } from 'next/server';
+import { GiveawayStore } from '../src/lib/giveaway-store';
+import { MemoryGiveawayRepository } from '../src/lib/repository/memory-repository';
+import { GET as giveawaysGet } from '../src/app/api/giveaways/route';
+import { defaultSessionStore, SESSION_COOKIE_NAME } from '../src/lib/auth/session';
+import { DEFAULT_FILTER_RULES } from '../src/core/types/giveaway';
+
+describe('Phase 2.2.3 Claude PoC: GET /api/giveaways IDOR & Scoped Query Gate', () => {
+  let memoryRepo: MemoryGiveawayRepository;
+
+  const userA = { id: 'usr_organizer_alpha', vkUserId: '11111', firstName: 'Alice' };
+  const userB = { id: 'usr_organizer_beta', vkUserId: '22222', firstName: 'Bob' };
+  const userEmpty = { id: 'usr_organizer_empty', vkUserId: '33333', firstName: 'Charlie' };
+
+  let sessionA: string;
+  let sessionB: string;
+  let sessionEmpty: string;
+
+  beforeEach(async () => {
+    memoryRepo = new MemoryGiveawayRepository();
+    GiveawayStore.setRepository(memoryRepo);
+
+    defaultSessionStore.clear();
+    sessionA = await defaultSessionStore.createSession(userA);
+    sessionB = await defaultSessionStore.createSession(userB);
+    sessionEmpty = await defaultSessionStore.createSession(userEmpty);
+
+    // Populate giveaways for User A
+    await GiveawayStore.create({
+      sourceUrl: 'https://vk.com/wall-10_100',
+      post: {
+        platform: 'VK',
+        ownerId: '-10',
+        postId: '100',
+        sourceUrl: 'https://vk.com/wall-10_100',
+        title: 'Secret Giveaway of Alice',
+        likesCount: 10,
+        commentsCount: 2,
+        repostsCount: 0,
+      },
+      filterRules: DEFAULT_FILTER_RULES,
+      organizerId: userA.id,
+    });
+
+    // Populate giveaways for User B
+    await GiveawayStore.create({
+      sourceUrl: 'https://vk.com/wall-20_200',
+      post: {
+        platform: 'VK',
+        ownerId: '-20',
+        postId: '200',
+        sourceUrl: 'https://vk.com/wall-20_200',
+        title: 'Confidential Giveaway of Bob',
+        likesCount: 50,
+        commentsCount: 15,
+        repostsCount: 5,
+      },
+      filterRules: DEFAULT_FILTER_RULES,
+      organizerId: userB.id,
+    });
+  });
+
+  it('Claude PoC Reproduction: anonymous GET /api/giveaways is rejected with 401 Unauthorized', async () => {
+    const req = new NextRequest('http://localhost:3000/api/giveaways');
+    const res = await giveawaysGet(req);
+
+    expect(res.status).toBe(401);
+    const body = await res.json();
+    expect(body.error?.message).toMatch(/authentication required/i);
+    // Crucial: No giveaways leaked to anonymous attacker
+    expect(body.giveaways).toBeUndefined();
+  });
+
+  it('User A list returns strictly User A giveaways (no User B records leaked)', async () => {
+    const req = new NextRequest('http://localhost:3000/api/giveaways', {
+      headers: { cookie: `${SESSION_COOKIE_NAME}=${sessionA}` },
+    });
+    const res = await giveawaysGet(req);
+
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body.success).toBe(true);
+    expect(body.giveaways).toHaveLength(1);
+
+    const gw = body.giveaways[0];
+    expect(gw.organizerId).toBe(userA.id);
+    expect(gw.title).toBe('Secret Giveaway of Alice');
+
+    // Ensure User B information is completely absent
+    expect(JSON.stringify(body)).not.toContain('Bob');
+    expect(JSON.stringify(body)).not.toContain('Confidential Giveaway of Bob');
+    expect(JSON.stringify(body)).not.toContain('wall-20_200');
+  });
+
+  it('User B list returns strictly User B giveaways (no User A records leaked)', async () => {
+    const req = new NextRequest('http://localhost:3000/api/giveaways', {
+      headers: { cookie: `${SESSION_COOKIE_NAME}=${sessionB}` },
+    });
+    const res = await giveawaysGet(req);
+
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body.success).toBe(true);
+    expect(body.giveaways).toHaveLength(1);
+
+    const gw = body.giveaways[0];
+    expect(gw.organizerId).toBe(userB.id);
+    expect(gw.title).toBe('Confidential Giveaway of Bob');
+
+    // Ensure User A information is completely absent
+    expect(JSON.stringify(body)).not.toContain('Alice');
+    expect(JSON.stringify(body)).not.toContain('Secret Giveaway of Alice');
+    expect(JSON.stringify(body)).not.toContain('wall-10_100');
+  });
+
+  it('empty account receives empty array [] without errors', async () => {
+    const req = new NextRequest('http://localhost:3000/api/giveaways', {
+      headers: { cookie: `${SESSION_COOKIE_NAME}=${sessionEmpty}` },
+    });
+    const res = await giveawaysGet(req);
+
+    expect(res.status).toBe(200);
+    const body = await res.json();
+    expect(body.success).toBe(true);
+    expect(body.giveaways).toEqual([]);
+    expect(body.totalCount).toBe(0);
+  });
+
+  it('Repository level test: listGiveawaysSummary filters directly by organizerId', async () => {
+    const summariesA = await memoryRepo.listGiveawaysSummary(userA.id);
+    expect(summariesA).toHaveLength(1);
+    expect(summariesA[0].organizerId).toBe(userA.id);
+
+    const summariesB = await memoryRepo.listGiveawaysSummary(userB.id);
+    expect(summariesB).toHaveLength(1);
+    expect(summariesB[0].organizerId).toBe(userB.id);
+
+    const summariesEmpty = await memoryRepo.listGiveawaysSummary(userEmpty.id);
+    expect(summariesEmpty).toHaveLength(0);
+  });
+});
diff --git a/tests/oauth-concurrency.test.ts b/tests/oauth-concurrency.test.ts
new file mode 100644
index 0000000..6eb01bf
--- /dev/null
+++ b/tests/oauth-concurrency.test.ts
@@ -0,0 +1,70 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import { MemoryOAuthTransactionStore } from '../src/lib/auth/oauth-state';
+
+describe('Phase 2.2.3 OAuth Atomic Consume & 100-Concurrent Race Gate', () => {
+  let store: MemoryOAuthTransactionStore;
+
+  beforeEach(() => {
+    store = new MemoryOAuthTransactionStore();
+  });
+
+  it('100 concurrent consumeTransaction attempts on the same state result in exactly 1 success and 99 failures', async () => {
+    // 1. Create a single valid transaction
+    const { state, codeVerifier } = await store.createTransaction({
+      redirectTarget: '/giveaways/new',
+      ttlMs: 5 * 60 * 1000,
+    });
+
+    // 2. Launch 100 concurrent consume requests
+    const attempts = Array.from({ length: 100 }, async (_, index) => {
+      try {
+        const result = await store.consumeTransaction(state);
+        return { success: true, verifier: result.codeVerifier, index };
+      } catch (err: any) {
+        return { success: false, error: err.message, index };
+      }
+    });
+
+    const results = await Promise.all(attempts);
+
+    const successful = results.filter(r => r.success);
+    const failed = results.filter(r => !r.success);
+
+    // Invariant: Exactly 1 consume succeeds
+    expect(successful).toHaveLength(1);
+    expect(failed).toHaveLength(99);
+
+    // Invariant: The winning consume got the exact codeVerifier
+    expect(successful[0].verifier).toBe(codeVerifier);
+
+    // Invariant: Subsequent sequential consume also fails
+    await expect(store.consumeTransaction(state)).rejects.toThrow(/already consumed/i);
+  });
+
+  it('reused state is immediately rejected with unauthorized error', async () => {
+    const { state } = await store.createTransaction();
+
+    // First consume succeeds
+    const first = await store.consumeTransaction(state);
+    expect(first.codeVerifier).toBeDefined();
+
+    // Second consume fails
+    await expect(store.consumeTransaction(state)).rejects.toThrow(/already consumed/i);
+  });
+
+  it('expired state cannot be consumed', async () => {
+    const { state } = await store.createTransaction({ ttlMs: -1000 }); // Expired in the past
+
+    await expect(store.consumeTransaction(state)).rejects.toThrow(/expired/i);
+  });
+
+  it('invalidateTransaction deletes state cleanly on error or cancellation', async () => {
+    const { state } = await store.createTransaction();
+
+    const deleted = await store.invalidateTransaction(state);
+    expect(deleted).toBe(true);
+
+    // State can no longer be consumed
+    await expect(store.consumeTransaction(state)).rejects.toThrow(/not found/i);
+  });
+});
diff --git a/tests/origin-and-csrf-gate.test.ts b/tests/origin-and-csrf-gate.test.ts
new file mode 100644
index 0000000..e59942a
--- /dev/null
+++ b/tests/origin-and-csrf-gate.test.ts
@@ -0,0 +1,120 @@
+import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { NextRequest } from 'next/server';
+import { validateCsrfOrigin } from '../src/lib/auth/csrf-guard';
+import { getAppBaseUrl, getVkRedirectUri } from '../src/lib/auth/app-config';
+import { GET as vkStartGet, oauthStartRateLimiter } from '../src/app/api/auth/vk/start/route';
+
+describe('Phase 2.2.3 Origin, CSRF Trusted Host & Rate Limiting Gate', () => {
+  const originalEnv = process.env;
+
+  beforeEach(() => {
+    process.env = { ...originalEnv };
+  });
+
+  afterEach(() => {
+    process.env = originalEnv;
+  });
+
+  describe('Production Base URL & VK_REDIRECT_URI Fail-Fast Policy', () => {
+    it('fails fast in production when APP_BASE_URL is missing', () => {
+      process.env.NODE_ENV = 'production';
+      delete process.env.APP_BASE_URL;
+
+      expect(() => getAppBaseUrl()).toThrow(/APP_BASE_URL environment variable is strictly required in production/i);
+    });
+
+    it('fails fast in production when APP_BASE_URL is not HTTPS', () => {
+      process.env.NODE_ENV = 'production';
+      process.env.APP_BASE_URL = 'http://insecure-http-url.com';
+
+      expect(() => getAppBaseUrl()).toThrow(/must be a valid HTTPS URL in production/i);
+    });
+
+    it('fails fast in production when VK_REDIRECT_URI is missing', () => {
+      process.env.NODE_ENV = 'production';
+      process.env.APP_BASE_URL = 'https://randomayzer.org';
+      delete process.env.VK_REDIRECT_URI;
+
+      expect(() => getVkRedirectUri()).toThrow(/VK_REDIRECT_URI environment variable is strictly required in production/i);
+    });
+
+    it('accepts valid HTTPS configuration in production', () => {
+      process.env.NODE_ENV = 'production';
+      process.env.APP_BASE_URL = 'https://randomayzer.org';
+      process.env.VK_REDIRECT_URI = 'https://randomayzer.org/api/auth/vk/callback';
+
+      expect(getAppBaseUrl()).toBe('https://randomayzer.org');
+      expect(getVkRedirectUri()).toBe('https://randomayzer.org/api/auth/vk/callback');
+    });
+  });
+
+  describe('CSRF Trusted Host & Host-Spoofing Immunity', () => {
+    it('rejects attacker sending evil Origin even if attacker injects spoofed X-Forwarded-Host', () => {
+      process.env.NODE_ENV = 'production';
+      process.env.APP_BASE_URL = 'https://trusted-randomayzer.org';
+
+      const req = new NextRequest('http://localhost/api/auth/logout', {
+        method: 'POST',
+        headers: {
+          origin: 'https://evil.com',
+          'x-forwarded-host': 'evil.com', // Spoofed header
+        },
+      });
+
+      expect(() => validateCsrfOrigin(req)).toThrow(/CSRF origin mismatch/i);
+    });
+
+    it('rejects cross-site Sec-Fetch-Site requests', () => {
+      const req = new NextRequest('http://localhost/api/auth/logout', {
+        method: 'POST',
+        headers: {
+          origin: 'https://trusted-randomayzer.org',
+          'sec-fetch-site': 'cross-site',
+        },
+      });
+
+      expect(() => validateCsrfOrigin(req)).toThrow(/cross-site origin rejected/i);
+    });
+
+    it('accepts valid origin matching configured trusted host', () => {
+      process.env.NODE_ENV = 'production';
+      process.env.APP_BASE_URL = 'https://trusted-randomayzer.org';
+
+      const req = new NextRequest('https://trusted-randomayzer.org/api/auth/logout', {
+        method: 'POST',
+        headers: {
+          origin: 'https://trusted-randomayzer.org',
+          'sec-fetch-site': 'same-origin',
+        },
+      });
+
+      expect(() => validateCsrfOrigin(req)).not.toThrow();
+    });
+  });
+
+  describe('OAuth Start Rate Limiter', () => {
+    it('rate limits burst requests to GET /api/auth/vk/start', async () => {
+      oauthStartRateLimiter.clear();
+
+      const ip = '198.51.100.42';
+
+      // 10 allowed requests
+      for (let i = 0; i < 10; i++) {
+        const req = new NextRequest('http://localhost:3000/api/auth/vk/start', {
+          headers: { 'x-forwarded-for': ip },
+        });
+        const res = await vkStartGet(req);
+        expect(res.status).toBe(307); // Temporary redirect to VK
+      }
+
+      // 11th request in the same window -> 429 Too Many Requests
+      const blockedReq = new NextRequest('http://localhost:3000/api/auth/vk/start', {
+        headers: { 'x-forwarded-for': ip },
+      });
+      const blockedRes = await vkStartGet(blockedReq);
+      expect(blockedRes.status).toBe(429);
+      const body = await blockedRes.json();
+      expect(body.error?.message).toMatch(/rate limit exceeded/i);
+    });
+  });
+});