# Authentication System Pattern

**Pattern Type**: Authentication System
**Confidence**: 0.85
**Expected Complexity**: 6.0-8.0

## Pattern Characteristics

This directive matches the **Authentication System** pattern because it involves:

1. **Security critical components** (authentication, authorization)
2. **Multiple auth methods** (session-based + JWT)
3. **Migration path** (backwards compatibility requirement)
4. **Middleware integration** (request validation, token verification)
5. **State coordination** (session validity during migration)

## Expected Systems

- **API Layer**: New `/auth/token` endpoint, JWT issuance logic
- **Middleware**: Token validation, session verification, dual-mode auth
- **Database**: Token storage or session migration (depending on implementation)
- **Documentation**: Migration guide for API consumers

## Expected Modifiers

- **Security**: Critical (authentication/authorization logic)
- **State Coordination**: Medium (dual auth during migration)
- **Breaking Changes**: Low (backwards compatible via 30-day window)
- **Data Migration**: Low (session preservation, not schema changes)

## Recommended Splitting

### Binary Split (2 children)

**Recommended for clean separation of concerns**:

```
Parent: JWT Authentication Implementation
├── Child 0: Backend - JWT infrastructure
│   ├── Token generation/validation
│   ├── Middleware integration
│   └── Session compatibility layer
└── Child 1: Documentation & Migration
    ├── API migration guide
    ├── Client integration examples
    └── Rollback procedures
```

### Ternary Split (3 children)

**Alternative if backend work is substantial**:

```
Parent: JWT Authentication Implementation
├── Child 0: Core Auth - Token lifecycle
│   ├── JWT generation
│   ├── Token validation
│   └── Refresh token flow
├── Child 1: Integration - Middleware
│   ├── Dual-mode middleware
│   ├── Session compatibility
│   └── Auth header parsing
└── Child 2: Migration - Transition plan
    ├── API consumer guide
    ├── Testing procedures
    └── Rollback strategy
```

## Key Considerations

### Security Concerns
- Token secret management (environment variables, not hardcoded)
- Expiration policies (access token: 15m, refresh token: 7d)
- Secure token storage on client side
- HTTPS enforcement

### Migration Window
- 30-day dual-mode operation
- Monitoring for session vs JWT usage
- Gradual rollout to API consumers
- Metrics for adoption tracking

### Testing Strategy
- Unit tests for token generation/validation
- Integration tests for dual-mode middleware
- Security tests for common attack vectors (replay, tampering)
- Load tests for token validation performance

## Expected Conflicts

### Likely Conflicts
- **Interface Mismatch**: Middleware signature changes vs existing auth flow
- **Assumption Violation**: Token storage strategy (DB vs stateless JWT)

### Unlikely Conflicts
- **File Overlap**: Backend and docs touch different files
- **Decision Contradiction**: Clear pattern with established best practices

## Verification Commands

```bash
# Test JWT generation
curl -X POST http://localhost:8000/auth/token \
  -H "Content-Type: application/json" \
  -d '{"username": "test", "password": "test"}'

# Test JWT authentication
curl http://localhost:8000/api/protected \
  -H "Authorization: Bearer <token>"

# Test session authentication (backwards compatibility)
curl http://localhost:8000/api/protected \
  -H "Cookie: session_id=<session>"

# Run security tests
pytest tests/auth/test_jwt_security.py -v
```

## Success Criteria

1. `/auth/token` endpoint returns valid JWT
2. Protected routes accept both JWT and session auth
3. Existing session-based clients continue working
4. Migration guide published for API consumers
5. Security tests pass (no vulnerabilities)
6. 30-day migration window enforced in code
