# Implementation Tasks

## 1. Database Schema Updates
- [ ] 1.1 Create database migration script
  - Add `external_user_id` column (VARCHAR 255)
  - Add `display_name` column (VARCHAR 255)
  - Add `azure_email` column (VARCHAR 255)
  - Add `last_token_refresh` column (DATETIME)
  - Mark `hashed_password` as nullable (for gradual migration)
- [ ] 1.2 Update User model
  - Add new fields to SQLAlchemy model
  - Update model relationships if needed
  - Add migration version with Alembic
- [ ] 1.3 Create user sync mechanism
  - Script to map existing users to external IDs
  - Handle users without external accounts
  - Backup existing user data

## 2. Configuration Management
- [ ] 2.1 Update environment configuration
  - Add `EXTERNAL_AUTH_API_URL` to `.env.local`
  - Add `EXTERNAL_AUTH_ENDPOINT` configuration
  - Add `EXTERNAL_AUTH_TIMEOUT` setting
  - Add `USE_EXTERNAL_AUTH` feature flag
  - Add `TOKEN_REFRESH_BUFFER` setting
- [ ] 2.2 Update Settings class
  - Add external auth settings to `backend/app/core/config.py`
  - Add validation for new configuration values
  - Implement feature flag logic

## 3. External API Integration Service
- [ ] 3.1 Create auth API client
  - Implement `backend/app/services/external_auth_service.py`
  - Create async HTTP client for API calls
  - Implement request/response models
  - Add proper error handling and logging
- [ ] 3.2 Implement authentication methods
  - `authenticate_user()` - Call external API
  - `validate_token()` - Verify token validity
  - `refresh_token()` - Handle token refresh
  - `get_user_info()` - Fetch user details
- [ ] 3.3 Add resilience patterns
  - Implement retry logic with exponential backoff
  - Add circuit breaker pattern
  - Implement timeout handling
  - Add fallback mechanisms

## 4. Backend Authentication Updates
- [ ] 4.1 Modify login endpoint
  - Update `backend/app/api/v1/endpoints/auth.py`
  - Route to external API based on feature flag
  - Handle both authentication modes during transition
  - Return appropriate token format
- [ ] 4.2 Update token validation
  - Modify `backend/app/core/security.py`
  - Support both local and external tokens
  - Implement token type detection
  - Update JWT validation logic
- [ ] 4.3 Update authentication dependencies
  - Modify `backend/app/core/auth.py`
  - Update `get_current_user()` dependency
  - Handle external user information
  - Implement proper user context

## 5. Session and Token Management
- [ ] 5.1 Implement token storage
  - Store external tokens securely
  - Implement token encryption at rest
  - Handle multiple token types (access, ID, refresh)
- [ ] 5.2 Create token refresh mechanism
  - Background task for token refresh
  - Refresh tokens before expiration
  - Update stored tokens atomically
  - Handle refresh failures gracefully
- [ ] 5.3 Session invalidation
  - Clear tokens on logout
  - Handle token revocation
  - Implement session timeout

## 6. Frontend Updates
- [ ] 6.1 Update authentication service
  - Modify `frontend/src/services/authService.ts`
  - Handle new token format
  - Store user display information
  - Implement token refresh on client side
- [ ] 6.2 Update auth store
  - Modify `frontend/src/stores/authStore.ts`
  - Store external user information
  - Update user display logic
  - Handle token expiration
- [ ] 6.3 Update UI components
  - Modify `frontend/src/components/Header.tsx`
  - Display user `name` instead of username
  - Show additional user information
  - Update login form if needed
- [ ] 6.4 Error handling
  - Handle external API errors
  - Display appropriate error messages
  - Implement retry UI for failures
  - Add loading states

## 7. Testing
- [ ] 7.1 Unit tests
  - Test external auth service
  - Test token validation
  - Test user information mapping
  - Test error scenarios
- [ ] 7.2 Integration tests
  - Test full authentication flow
  - Test token refresh mechanism
  - Test fallback scenarios
  - Test feature flag switching
- [ ] 7.3 Load testing
  - Test external API response times
  - Test system under high authentication load
  - Measure impact on performance
- [ ] 7.4 Security testing
  - Test token security
  - Verify HTTPS enforcement
  - Test rate limiting
  - Validate error message security

## 8. Migration Execution
- [ ] 8.1 Pre-migration preparation
  - Backup database
  - Document rollback procedure
  - Prepare user communication
  - Set up monitoring
- [ ] 8.2 Staged rollout
  - Enable for test users first
  - Monitor for issues
  - Gradually increase user percentage
  - Collect feedback
- [ ] 8.3 Post-migration validation
  - Verify all users can login
  - Check audit logs
  - Monitor error rates
  - Validate performance metrics

## 9. Documentation
- [ ] 9.1 Technical documentation
  - Update API documentation
  - Document authentication flow
  - Update deployment guide
  - Create troubleshooting guide
- [ ] 9.2 User documentation
  - Update login instructions
  - Document new features
  - Create FAQ for common issues
- [ ] 9.3 Operations documentation
  - Document monitoring points
  - Create runbook for issues
  - Document rollback procedure

## 10. Monitoring and Observability
- [ ] 10.1 Add monitoring metrics
  - Authentication success/failure rates
  - External API response times
  - Token refresh success rate
  - Error rate monitoring
- [ ] 10.2 Implement logging
  - Log all authentication attempts
  - Log external API calls
  - Log token operations
  - Structured logging for analysis
- [ ] 10.3 Create alerts
  - Alert on high failure rates
  - Alert on external API unavailability
  - Alert on token refresh failures
  - Alert on unusual patterns

## 11. Cleanup (Post-Stabilization)
- [ ] 11.1 Remove legacy code
  - Remove local authentication code (after stable period)
  - Remove unused database columns
  - Clean up configuration
- [ ] 11.2 Optimize performance
  - Implement caching where appropriate
  - Optimize database queries
  - Review and optimize API calls