---
phase: 01-core-infrastructure-security
plan: 03
subsystem: security
tags: [slowapi, fastapi-csrf-protect, rate-limiting, cors, security-headers, middleware]

# Dependency graph
requires:
  - phase: 01-01
    provides: FastAPI application structure, pydantic-settings configuration
  - phase: 01-02
    provides: PostgreSQL database, async session factory, get_db dependency
provides:
  - Rate limiting at 100 requests/minute per IP
  - CSRF protection with secure cookie configuration
  - Security headers middleware (HSTS, X-Frame-Options, X-XSS-Protection)
  - TrustedHostMiddleware for Host header validation
  - CORS configuration with credential support
  - Database health check endpoint at /api/v1/health/db
affects: [01-04, 01-05, 02, 03]

# Tech tracking
tech-stack:
  added: [slowapi, fastapi-csrf-protect]
  patterns: [security-middleware-stack, rate-limit-exempt-decorator, dependency-injection-for-csrf]

key-files:
  created:
    - backend/app/core/security.py
    - backend/app/api/deps.py
  modified:
    - backend/app/main.py
    - backend/app/api/v1/endpoints/health.py

key-decisions:
  - "Security headers applied via custom middleware (Starlette @app.middleware pattern)"
  - "Rate limiting uses in-memory storage for development, Redis URL configurable for production"
  - "Health endpoints exempt from rate limiting via @limiter.exempt decorator"
  - "CSRF validation available as optional dependency injection pattern"

patterns-established:
  - "Middleware ordering: TrustedHost (outermost) -> CORS -> Rate limiting -> Security headers (innermost)"
  - "deps.py centralizes FastAPI dependencies with re-exports for cleaner imports"
  - "Database health check with SELECT 1 query pattern"

# Metrics
duration: 3min
completed: 2026-01-25
---

# Phase 01 Plan 03: Security Middleware Stack Summary

**FastAPI security middleware with 100/min rate limiting, CSRF protection, trusted host validation, CORS, and security headers (HSTS, X-Frame-Options, X-XSS-Protection, Referrer-Policy)**

## Performance

- **Duration:** 3 min
- **Started:** 2026-01-25T20:17:05Z
- **Completed:** 2026-01-25T20:20:07Z
- **Tasks:** 2
- **Files modified:** 4 (plus 1 migration file linting fix)

## Accomplishments

- Rate limiting configured at 100 requests/minute using slowapi with in-memory storage
- CSRF protection configured with secure cookie settings (httponly, samesite=lax, secure=true)
- Security headers middleware adds HSTS, X-Content-Type-Options, X-Frame-Options, X-XSS-Protection, Referrer-Policy
- TrustedHostMiddleware rejects requests with invalid Host headers (returns 400)
- Database health check endpoint verifies PostgreSQL connectivity

## Task Commits

Each task was committed atomically:

1. **Task 1: Configure rate limiting and CSRF protection** - `81486fc` (feat)
2. **Task 2: Apply security middleware and update health endpoint** - `0d1a008` (feat)

## Files Created/Modified

- `backend/app/core/security.py` - Rate limiter and CSRF settings configuration
- `backend/app/api/deps.py` - Dependency injection utilities with get_db re-export and CSRF validation
- `backend/app/main.py` - Security middleware stack applied in correct order
- `backend/app/api/v1/endpoints/health.py` - Database health check endpoint with rate limit exemption

## Decisions Made

- Used Starlette's @app.middleware("http") for security headers instead of separate middleware class (simpler for static headers)
- Health endpoints marked @limiter.exempt to avoid rate limiting health checks from monitoring systems
- CSRF validation is optional dependency injection pattern (validate_csrf) rather than middleware, allowing per-endpoint control
- Used get_db re-export pattern in deps.py for cleaner import paths in endpoints

## Deviations from Plan

### Auto-fixed Issues

**1. [Rule 3 - Blocking] Fixed ruff linting errors in migration file**
- **Found during:** Task 2 (ruff check backend/)
- **Issue:** Pre-existing migration file had trailing whitespace, long lines, and old Union syntax
- **Fix:** Reformatted file to comply with ruff rules (line length, modern type hints)
- **Files modified:** backend/alembic/versions/de1460a760b0_create_build_table.py
- **Verification:** `ruff check backend/` passes with no errors
- **Committed in:** 0d1a008 (Task 2 commit)

---

**Total deviations:** 1 auto-fixed (1 blocking)
**Impact on plan:** Linting fix was necessary for verification to pass. No scope creep.

## Issues Encountered

None - plan executed as expected.

## User Setup Required

None - no external service configuration required. Rate limiting uses in-memory storage by default.

## Next Phase Readiness

- Security middleware stack complete and verified
- Ready for 01-04-PLAN.md (Caddy reverse proxy and automatic HTTPS)
- CSRF protection configured but not enforced on endpoints yet (ready for form submission protection when needed)

---
*Phase: 01-core-infrastructure-security*
*Completed: 2026-01-25*