Finishes functional design for unit 0 (back-end changes before front-end work)

2026-06-18 21:40:45 +02:00
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+# NFR Requirements — Unit 0: Backend Prerequisites
+
+## NFR-U0-01: Security — httpOnly Cookie (SECURITY-12)
+- Refresh token MUST be stored in an httpOnly, Secure (request.IsHttps), SameSite=Strict cookie
+- Access token MUST NOT be returned in persistent storage; only in response body and in-memory on client
+- See `business-rules.md` BR-U0-02, BR-U0-03 for detailed cookie specification
+
+## NFR-U0-02: Security — CORS (SECURITY-08)
+- CORS MUST use explicit origin allowlist from configuration — no wildcard origins
+- `AllowCredentials()` MUST be set to allow the refresh token cookie to be sent cross-origin
+- CORS middleware MUST be registered before `UseAuthentication` in the pipeline
+- An empty `AllowedOrigins` array in production configuration is a safe default (no SPA access)
+
+## NFR-U0-03: Security — Rate Limiting (SECURITY-11)
+- The `POST /api/v1/auth/login` and `POST /api/v1/auth/refresh` endpoints MUST have rate limiting
+- **Implementation**: ASP.NET Core built-in `RateLimiter` middleware (available in .NET 7+)
+- **Policy**: Fixed window — max **5 requests per 1 minute per IP address** on login endpoint
+- **Policy**: Sliding window — max **20 requests per 1 minute per IP address** on refresh endpoint
+- Exceeded rate limit returns `429 Too Many Requests`
+- Rate limit headers (`Retry-After`) MUST be included in 429 responses
+- Configuration stored in `appsettings.json → RateLimiting` section
+
+## NFR-U0-04: Reliability — Refresh Token Lifetime
+- Refresh token lifetime: **7 days** (unchanged from current default)
+- After expiry, the user must re-authenticate via the login page
+- Refresh token rotation is already implemented — each refresh issues a new token
+
+## NFR-U0-05: Error Response Format (SECURITY-09, SECURITY-15)
+- ALL authentication error responses MUST use **RFC 9457 ProblemDetails** format:
+  ```json
+  {
+    "type": "https://tools.ietf.org/html/rfc7235#section-3.1",
+    "title": "Unauthorized",
+    "status": 401,
+    "detail": "Invalid credentials."
+  }
+  ```
+- Error messages MUST be generic — do NOT reveal whether email or password was wrong
+- Error messages MUST NOT expose internal details (stack traces, exception types, DB details)
+- `asp-problem-details` behavior is already partially handled by `GlobalExceptionHandler`; auth-specific errors may need explicit `ProblemDetails` returns in `AuthController`
+
+## NFR-U0-06: Maintainability
+- Rate limiting configuration (window size, request limits) stored in `appsettings.json` — configurable without code changes
+- CORS origins stored in `appsettings.json` — configurable per environment
+- No magic strings for cookie name or policy name — use constants
+
+## NFR-U0-07: Test Coverage
+- Unit tests for `AuthController` must be updated to cover:
+  - Cookie is set on successful login/refresh
+  - Cookie is cleared on revoke
+  - 401 returned when cookie is missing on refresh
+  - Rate limit behavior (mock rate limiter)
+- Existing `AuthService` unit tests remain valid (service signature unchanged)