# CSRF Protection Implementation Summary

## Changes Made

### 1. Created CSRF Protection Library (`src/lib/csrf.ts`)
- Implements double-submit cookie pattern for CSRF protection
- Provides `withCSRFProtection` middleware wrapper for API routes
- Generates cryptographically secure tokens using Node.js crypto
- Validates tokens with timing-safe comparison to prevent timing attacks
- Checks Origin/Referer headers for same-origin validation

### 2. Created CSRF Token Endpoint (`src/app/api/auth/csrf/route.ts`)
- Generates and returns CSRF tokens for authenticated users
- Sets HttpOnly, SameSite=Strict cookie with the token
- Should be called after successful authentication

### 3. Created Client-Side CSRF Utilities (`src/lib/csrf-client.ts`)
- `getCSRFCookie()`: Retrieves CSRF token from browser cookies
- `fetchCSRFToken()`: Fetches new token from server endpoint
- `withCSRFToken()`: Adds CSRF token to fetch request headers
- `csrfFetch()`: Enhanced fetch with automatic CSRF protection
- `addCSRFTokenToFormData()`: Adds token to FormData for form submissions
- `initializeCSRF()`: Initializes CSRF after authentication

### 4. Protected API Routes
The following routes now have CSRF protection:

#### Payment Routes
- `/api/payments/create` - Payment creation (POST)

#### Authentication Routes
- `/api/auth/verify-email` - Email verification (POST)

#### AI Routes (state-changing operations)
- `/api/ai/generate-profile` - Profile generation (POST)
- `/api/ai/parse-profile-voice` - Voice profile parsing (POST)
- `/api/ai/transcribe-voice` - Audio transcription (POST)

### 5. Routes NOT Protected (GET/HEAD/OPTIONS or stateless)
- `/api/abn-lookup` - GET only, read-only operation
- `/api/company-logo` - GET only, read-only operation
- `/api/webhooks/stripe` - Webhook endpoint with its own signature verification

## Implementation Details

### CSRF Protection Method
Used **Option C: Double-submit cookie pattern** with the following features:
- Token stored in HttpOnly, SameSite=Strict cookie
- Token also sent in request header (`x-csrf-token`) or form field
- Server validates that both tokens match
- 24-hour token expiration

### Security Features
- Cryptographically secure random token generation
- Timing-safe token comparison
- Same-origin validation (configurable)
- Automatic protection for POST, PUT, DELETE methods
- Skip protection for safe methods (GET, HEAD, OPTIONS)

### Client Integration
- Tokens automatically included in fetch requests
- Form submissions include token in hidden field
- Token refresh capability after authentication

## Next Steps for Frontend Integration

1. Call `/api/auth/csrf` after successful login/signup
2. Use `csrfFetch()` instead of regular `fetch()` for API calls
3. Add CSRF token to forms using `addCSRFTokenToFormData()`
4. Include token in JSON requests via `withCSRFToken()`

## Testing

The implementation has been added to the codebase. To test:
1. Authenticate to get a session
2. Fetch CSRF token from `/api/auth/csrf`
3. Include token in subsequent POST/PUT/DELETE requests
4. Requests without valid tokens will return 403 Forbidden