feat: comprehensive ADR-structured design document template

Created production-ready design document template with 14 comprehensive sections:

**Structure:**
1. Executive Summary & Context
2. Requirements (Functional & Non-Functional)
3. Options Considered (with pros/cons/cost analysis)
4. Decision & Rationale (trade-offs, assumptions, review triggers)
5. Architecture (diagrams, components, data models, API contracts)
6. Implementation Plan (phases, dependencies, resources)
7. Risks & Mitigations (threat model, compliance)
8. Testing Strategy (unit, integration, e2e, performance)
9. Monitoring & Observability (metrics, alerts, dashboards)
10. Documentation & Training
11. Rollout Plan (feature flags, staged rollout, rollback)
12. Future Enhancements & Technical Debt
13. Acceptance Criteria
14. Appendices (research, meeting notes, changelog)

**Features:**
- Industry-standard ADR format
- Comprehensive examples throughout
- SQL schema examples
- API contract specifications
- ASCII architecture diagrams
- Risk matrices and threat models
- Rollout and rollback procedures
- META tokens for AI placeholder replacement

This template guides teams through complete technical design documentation
from problem statement to production rollout.

Addresses PROGRESS.md Stage 3 requirement: "Enhanced template with ADR structure"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>
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# Design — <FR id / Title>
<!--META
{
"kind": "design_document",
"tokens": ["FeatureId", "CreatedDate", "Title"]
}
-->
## Context & Goals
## Non-Goals & Constraints
## Options Considered
## Decision & Rationale
## Architecture Diagram(s)
## Risks & Mitigations
## Acceptance Criteria (measurable)
# 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)