# Feature Specification: CentralDB Extension for MFA Token Management

**Feature Branch**: `008-centraldb-mfa-tokens`  
**Created**: Thursday, December 19, 2025  
**Status**: Draft  
**Input**: Requirement to extend CentralDB to support garth token management for MFA flow in garminsync

## User Scenarios & Testing *(mandatory)*

### User Story 1 - Secure Garth Token Storage (Priority: P1)

As a GarminSync service, I want to securely store garth authentication tokens (OAuth1/OAuth2) in CentralDB so that users can maintain authenticated sessions across service restarts and authenticate with MFA-enabled accounts.

**Why this priority**: This is fundamental to the entire MFA authentication flow. Without secure token storage, users would need to re-authenticate on every service restart, defeating the purpose of persistent authentication sessions.

**Independent Test**: Can be fully tested by authenticating a user with garth tokens, restarting the service, and verifying that tokens are still available for that user.

**Acceptance Scenarios**:

1. **Given** a user successfully authenticates with garth, **When** tokens are received from garth, **Then** tokens are securely stored in CentralDB with appropriate encryption
2. **Given** garth tokens exist for a user in CentralDB, **When** the service requests tokens for that user, **Then** the tokens are retrieved and decrypted appropriately
3. **Given** invalid or expired garth tokens in CentralDB, **When** the service attempts to use them, **Then** appropriate error handling occurs and re-authentication is required
4. **Given** a user requests logout, **When** the logout process begins, **Then** associated garth tokens are securely removed from CentralDB

### User Story 2 - MFA Challenge Tracking (Priority: P2)

As an administrator of the CentralDB service, I want to track MFA challenges so that the system can properly manage multi-factor authentication flows and prevent abuse.

**Why this priority**: Critical for security and proper MFA flow management. Enables tracking of authentication attempts and prevents brute-force attacks.

**Independent Test**: Can be fully tested by initiating multiple MFA challenges and verifying they are properly tracked, validated, and cleaned up.

**Acceptance Scenarios**:

1. **Given** a user initiates MFA authentication, **When** the challenge is created, **Then** the challenge is stored in CentralDB with appropriate expiration time
2. **Given** an MFA challenge exists in CentralDB, **When** the correct MFA code is provided, **Then** the challenge is marked as completed and can be consumed
3. **Given** an MFA challenge exists in CentralDB, **When** the challenge expires, **Then** the challenge is no longer valid and cleaned up automatically
4. **Given** multiple failed MFA attempts for a challenge, **When** the limit is reached, **Then** the challenge is invalidated and the user must restart authentication

### User Story 3 - Session Management for MFA Flows (Priority: P3)

As a user of the GarminSync service, I want to have my MFA state preserved during the authentication flow so that the system properly tracks my authentication progress.

**Why this priority**: Improves user experience by maintaining authentication state across requests during MFA flow, especially for longer-running flows.

**Independent Test**: Can be fully tested by initiating an MFA flow, checking that the system properly tracks the state, and then completing the flow successfully.

**Acceptance Scenarios**:

1. **Given** a user begins MFA authentication, **When** the session is created, **Then** MFA state is properly recorded in CentralDB
2. **Given** an MFA session exists in CentralDB, **When** MFA is completed successfully, **Then** the session is updated to reflect MFA completion
3. **Given** an MFA session exists in CentralDB, **When** MFA fails or times out, **Then** the session is properly cleaned up

### Edge Cases

- What happens when garth token encryption/decryption fails in CentralDB?
- How does the system handle concurrent MFA attempts for the same user?
- What occurs if CentralDB is temporarily unavailable during authentication?
- How does the system handle very large numbers of MFA challenges (potential DoS)?
- What happens when garth token storage exceeds allocated quotas?

## Requirements *(mandatory)*

### Functional Requirements

- **FR-001**: CentralDB MUST provide secure storage for garth OAuth1 and OAuth2 tokens with encryption at rest
- **FR-002**: CentralDB MUST provide API endpoints for storing, retrieving, and deleting garth tokens 
- **FR-003**: CentralDB MUST track MFA challenges with type, expiration time, and validation status
- **FR-004**: CentralDB MUST enforce MFA challenge expiration and limit retry attempts
- **FR-005**: CentralDB MUST associate garth tokens with specific user accounts for proper access control
- **FR-006**: CentralDB MUST provide API endpoints for MFA challenge creation and validation
- **FR-007**: CentralDB MUST maintain user session state during MFA authentication flows
- **FR-008**: CentralDB MUST securely delete garth tokens when users log out or tokens expire
- **FR-009**: CentralDB MUST prevent replay attacks of valid MFA codes
- **FR-010**: CentralDB MUST log authentication attempts for security auditing purposes

### Key Entities

- **GarthToken**: Securely stored OAuth tokens (encrypted) with user association and metadata
- **MFAChallenge**: Tracks authentication challenges including type, destination, status, and expiration
- **UserSession**: Maintains session state during authentication flows, particularly MFA

## Success Criteria *(mandatory)*

### Measurable Outcomes

- **SC-001**: 100% of garth tokens are stored encrypted in CentralDB with FIPS-compliant encryption
- **SC-002**: Token retrieval operations complete within 100ms for 95% of requests
- **SC-003**: MFA challenge validation completes within 200ms for 95% of requests
- **SC-004**: CentralDB handles MFA flows for 10,000 concurrent users without performance degradation
- **SC-005**: MFA challenge security mechanisms prevent 99.9% of replay and brute-force attempts
- **SC-006**: 99.9% uptime for token storage/retrieval operations during MFA flows

## Assumptions

- CentralDB uses PostgreSQL or SQLite with appropriate security configurations
- garth token data follows standard OAuth token formats
- Encryption at rest is implemented using library-appropriate mechanisms
- Network communication between GarminSync service and CentralDB is secured
- Proper access controls exist between services to prevent unauthorized token access
- GarminSync service has appropriate permissions to access token storage endpoints