# Design Document: {Title} **Feature ID:** {FeatureId} **Status:** Draft **Created:** {CreatedDate} **Last Updated:** {CreatedDate} **Authors:** [To be filled by AI from discussion participants] **Reviewers:** [To be filled from discussion] --- ## Executive Summary [1-2 paragraph overview of the feature and this design's approach. What problem does this solve? What's the proposed solution at a high level?] --- ## 1. Context & Problem Statement ### Background [What is the current state? What pain points or opportunities led to this feature request?] ### Business Goals - [Goal 1: e.g., Reduce user onboarding time by 50%] - [Goal 2: e.g., Support 10,000 concurrent users] - [Goal 3: e.g., Enable third-party integrations] ### Success Metrics | Metric | Target | Measurement Method | |--------|--------|-------------------| | [e.g., Page load time] | [< 2s] | [Performance testing] | | [e.g., User satisfaction] | [> 4.5/5] | [Post-feature survey] | --- ## 2. Requirements ### Functional Requirements **Must Have (MVP):** - [ ] [FR-1: User can create account with email/password] - [ ] [FR-2: User can reset password via email] - [ ] [FR-3: User can log in with Google OAuth] **Should Have (Nice to Have):** - [ ] [FR-4: Remember me functionality] - [ ] [FR-5: Two-factor authentication] **Won't Have (Out of Scope):** - [FR-6: Social login with Facebook/Twitter (deferred to v2)] - [FR-7: Biometric authentication (platform limitations)] ### Non-Functional Requirements **Performance:** - Response time: < 200ms for API calls - Throughput: Support 1,000 requests/second - Database queries: < 50ms p95 **Security:** - Password hashing: bcrypt with salt - Token expiration: 1 hour for access, 7 days for refresh - Rate limiting: 10 failed login attempts = 15min lockout **Scalability:** - Horizontal scaling: Support 10+ app instances - Database: Read replicas for query performance - Caching: Redis for session storage **Reliability:** - Uptime: 99.9% SLA - Data durability: Daily backups with 30-day retention - Graceful degradation: Fallback to email-only if OAuth fails --- ## 3. Options Considered ### Option 1: [Name, e.g., "In-house Authentication System"] **Approach:** [Description of this option] **Pros:** - ✅ [Pro 1] - ✅ [Pro 2] **Cons:** - ❌ [Con 1] - ❌ [Con 2] **Cost/Complexity:** - Development: [X person-weeks] - Maintenance: [Y hours/month] - Infrastructure: [Z $/month] **Risk Assessment:** - [Risk 1: Security vulnerabilities - HIGH] - [Risk 2: Development timeline - MEDIUM] --- ### Option 2: [Name, e.g., "Third-Party Auth Service (Auth0)"] **Approach:** [Description] **Pros:** - ✅ [Pro 1] - ✅ [Pro 2] **Cons:** - ❌ [Con 1] - ❌ [Con 2] **Cost/Complexity:** - Development: [X person-weeks] - Maintenance: [Y hours/month] - Infrastructure: [Z $/month] **Risk Assessment:** - [Risk 1] - [Risk 2] --- ### Option 3: [Name, if applicable] [Repeat structure from Option 1/2] --- ## 4. Decision & Rationale ### Selected Approach: [Option Name] **Primary Reasons:** 1. [Reason 1: Aligns with technical stack] 2. [Reason 2: Lowest total cost of ownership] 3. [Reason 3: Fastest time to market] **Trade-offs Accepted:** - [Trade-off 1: Higher infrastructure costs vs. lower dev time] - [Trade-off 2: Vendor lock-in vs. managed service reliability] **Alternatives Rejected:** - **Option X** rejected because: [reason] - **Option Y** rejected because: [reason] **Key Assumptions:** - [Assumption 1: User growth will remain under 100K for next 12 months] - [Assumption 2: OAuth providers maintain 99.9% uptime] **When to Revisit:** - If user base exceeds 500K (cost model changes) - If OAuth vendor has >2 major outages in 6 months - After 1 year in production (reevaluate build vs. buy) --- ## 5. Architecture ### System Architecture Diagram ``` [Insert diagram here - can be ASCII art, PlantUML, or image link] Example: ┌─────────────┐ ┌──────────────┐ ┌─────────────┐ │ Browser │─────▶│ API Gateway │─────▶│ Auth │ │ │◀─────│ │◀─────│ Service │ └─────────────┘ └──────────────┘ └─────────────┘ │ │ │ ▼ │ ┌──────────────┐ │ │ User DB │ │ │ (Postgres) │ │ └──────────────┘ ▼ ┌──────────────┐ │ Session │ │ Store │ │ (Redis) │ └──────────────┘ ``` ### Component Breakdown **Component 1: [Name, e.g., "Authentication Service"]** - **Responsibility:** Handle user login, registration, token issuance - **Technology:** Node.js (Express), PassportJS - **Interfaces:** - REST API: `/auth/login`, `/auth/register`, `/auth/refresh` - Events: `user.logged_in`, `user.registered` - **Dependencies:** User DB, Session Store, Email Service **Component 2: [Name]** [Repeat structure] ### Data Models **User Table:** ```sql CREATE TABLE users ( id UUID PRIMARY KEY, email VARCHAR(255) UNIQUE NOT NULL, password_hash VARCHAR(255), oauth_provider VARCHAR(50), oauth_id VARCHAR(255), created_at TIMESTAMP DEFAULT NOW(), updated_at TIMESTAMP DEFAULT NOW(), INDEX idx_email (email), UNIQUE idx_oauth (oauth_provider, oauth_id) ); ``` **Session Table:** ```sql CREATE TABLE sessions ( id UUID PRIMARY KEY, user_id UUID REFERENCES users(id), access_token VARCHAR(500) NOT NULL, refresh_token VARCHAR(500), expires_at TIMESTAMP NOT NULL, created_at TIMESTAMP DEFAULT NOW() ); ``` ### API Contracts **POST /auth/register** ```json Request: { "email": "user@example.com", "password": "SecurePass123!", "name": "John Doe" } Response (201 Created): { "user_id": "uuid", "access_token": "jwt", "refresh_token": "jwt", "expires_in": 3600 } Errors: 400 - Invalid email format 409 - Email already registered 422 - Password too weak ``` **POST /auth/login** [Similar structure] --- ## 6. Implementation Plan ### Phases **Phase 1: Core Authentication (Week 1-2)** - [ ] Set up database schema - [ ] Implement email/password registration - [ ] Implement login endpoint - [ ] Add password hashing (bcrypt) - [ ] Write unit tests **Phase 2: OAuth Integration (Week 3)** - [ ] Integrate Google OAuth - [ ] Add OAuth callback handling - [ ] Link OAuth accounts to existing users - [ ] Test OAuth flow **Phase 3: Security Hardening (Week 4)** - [ ] Add rate limiting - [ ] Implement token refresh - [ ] Add password reset flow - [ ] Security audit **Phase 4: Testing & Deployment (Week 5)** - [ ] End-to-end testing - [ ] Load testing - [ ] Documentation - [ ] Production deployment ### Dependencies - **External:** - Google OAuth credentials (waiting on: Platform team) - Email service API key (waiting on: DevOps) - **Internal:** - User profile service (blocks: User settings feature) - Session management (required by: All authenticated endpoints) ### Resource Requirements - **Development:** 1 backend engineer (full-time, 5 weeks) - **Design:** 0.5 designer (mockups, 1 week) - **QA:** 0.5 QA engineer (testing, 1 week) - **Infrastructure:** $200/month (database + Redis) --- ## 7. Risks & Mitigations | Risk | Probability | Impact | Mitigation | |------|-------------|--------|------------| | OAuth provider downtime | Medium | High | Fallback to email auth; cache OAuth tokens | | Password breach | Low | Critical | Bcrypt + salt; enforce strong passwords; rate limit | | Database bottleneck | Medium | High | Add read replicas; implement caching | | Token theft | Medium | High | Short expiration; secure httpOnly cookies | ### Security Considerations **Threat Model:** - **Threat 1: Brute force attacks** → Mitigation: Rate limiting, CAPTCHA after 3 failures - **Threat 2: SQL injection** → Mitigation: Parameterized queries, ORM usage - **Threat 3: XSS in user data** → Mitigation: Input validation, output encoding **Compliance:** - GDPR: User data deletion within 30 days of request - CCPA: User data export API endpoint - SOC 2: Audit logging for all auth events --- ## 8. Testing Strategy ### Unit Tests - Password hashing/validation - Token generation/validation - Input validation logic - Coverage target: 90% ### Integration Tests - Registration flow (email + OAuth) - Login flow (email + OAuth) - Token refresh flow - Password reset flow ### End-to-End Tests - New user signup journey - Returning user login journey - OAuth account linking - Session expiration handling ### Performance Tests - Concurrent logins: 1,000 users/second - Database query performance: < 50ms p95 - API response time: < 200ms p95 --- ## 9. Monitoring & Observability ### Metrics to Track **Business Metrics:** - Daily active users (DAU) - Registration conversion rate - OAuth vs. email signup ratio **Technical Metrics:** - API response time (p50, p95, p99) - Error rate by endpoint - Database connection pool utilization - Cache hit rate ### Alerts - Error rate > 5% for 5 minutes → Page on-call engineer - Response time p95 > 500ms → Slack warning - Failed login attempts > 100/min → Slack + investigate ### Dashboards - Real-time: Login success/failure rates, active sessions - Daily: User growth, OAuth provider breakdown - Weekly: Performance trends, error analysis --- ## 10. Documentation & Training ### User-Facing Documentation - [ ] Registration guide - [ ] Password reset guide - [ ] OAuth connection guide - [ ] Security best practices ### Developer Documentation - [ ] API reference (OpenAPI spec) - [ ] Local development setup - [ ] Testing guide - [ ] Deployment runbook ### Training Materials - [ ] Team demo of authentication flow - [ ] Security review session - [ ] Runbook walkthrough for on-call engineers --- ## 11. Rollout Plan ### Feature Flags ```yaml feature_flags: auth_email_registration: true auth_google_oauth: false # Enable after testing auth_password_reset: false # Enable in phase 2 ``` ### Rollout Stages 1. **Internal Alpha (Week 1)** - Deploy to staging - Team testing (10 users) - Fix critical bugs 2. **Beta (Week 2)** - Deploy to 10% of production traffic - Monitor error rates - Collect user feedback 3. **General Availability (Week 3)** - Ramp to 50%, then 100% - Enable OAuth - Sunset old authentication system (Week 4) ### Rollback Plan - **Trigger:** Error rate > 10% or critical security issue - **Procedure:** 1. Disable feature flag 2. Route traffic to old system 3. Incident post-mortem within 24 hours - **RTO:** 5 minutes (time to disable flag) - **RPO:** 0 (no data loss) --- ## 12. Future Enhancements ### Deferred to v2 - Two-factor authentication (SMS, TOTP) - Social login (Facebook, Twitter, GitHub) - Biometric authentication - SSO for enterprise customers ### Technical Debt Accepted - [Debt 1: Monolithic auth service - plan to split into microservices after 100K users] - [Debt 2: In-memory session cache - migrate to distributed cache under high load] --- ## 13. Acceptance Criteria This design is considered complete and ready for implementation when: - [x] All stakeholders have reviewed and approved - [ ] Security team has completed threat model review - [ ] At least 2 technical reviewers have signed off - [ ] All "Must Have" functional requirements are addressed - [ ] Performance targets are achievable (validated by load test plan) - [ ] Rollback plan is documented and tested - [ ] Cost estimate approved by finance --- ## 14. Appendices ### Appendix A: Research & References - [Link to competitive analysis] - [Link to user research findings] - [Link to technology evaluation matrix] ### Appendix B: Meeting Notes **Design Review 1 (YYYY-MM-DD):** - Attendees: [Names] - Decisions: [Key decisions] - Action items: [Follow-ups] ### Appendix C: Change Log | Date | Author | Change | |------|--------|--------| | {CreatedDate} | AI_Claude | Initial draft from feature discussion | | | | | --- **Document Status:** 🟡 Draft - Awaiting Review **Next Review Date:** [YYYY-MM-DD] **Related Documents:** - Feature Discussion: `../discussions/design.discussion.md` - Implementation Plan: `../implementation/plan.md` (created after approval)