Kiro Spec Writing Guide

# Requirements

## User Registration
WHEN a user submits valid registration data THE SYSTEM SHALL create a new user account
WHEN a user submits an email that already exists THE SYSTEM SHALL display "Email already registered" error
WHEN a user submits invalid email format THE SYSTEM SHALL display email validation error

## User Login  
WHEN a user enters correct credentials THE SYSTEM SHALL authenticate and redirect to dashboard
WHEN a user enters incorrect password THE SYSTEM SHALL display "Invalid credentials" error
WHEN a user fails login 3 times THE SYSTEM SHALL temporarily lock the account

# Shopping Cart Requirements

## Adding Items
WHEN a user clicks "Add to Cart" on an available product THE SYSTEM SHALL add the item to their cart
WHEN a user adds an item that exceeds stock quantity THE SYSTEM SHALL limit quantity to available stock
WHEN a user adds the same item multiple times THE SYSTEM SHALL increment the quantity

## Cart Persistence
WHEN a logged-in user adds items to cart THE SYSTEM SHALL persist cart across sessions
WHEN a guest user adds items to cart THE SYSTEM SHALL store cart in browser session
WHEN a guest user logs in with existing cart THE SYSTEM SHALL merge guest cart with user cart

## Checkout Process
WHEN a user proceeds to checkout with valid items THE SYSTEM SHALL display order summary
WHEN a user attempts checkout with out-of-stock items THE SYSTEM SHALL remove unavailable items and notify user
WHEN payment processing fails THE SYSTEM SHALL preserve cart contents and display error message

# Design Document: User Authentication

## Architecture Overview
```
Frontend (React) → API Gateway → Auth Service → Database
                              ↓
                         JWT Token Service
```

## Data Models

### User Schema
```typescript
interface User {
  id: string;
  email: string;
  passwordHash: string;
  createdAt: Date;
  lastLoginAt?: Date;
  isLocked: boolean;
  failedLoginAttempts: number;
}
```

### Session Schema  
```typescript
interface Session {
  id: string;
  userId: string;
  token: string;
  expiresAt: Date;
  createdAt: Date;
}
```

## API Endpoints

### POST /auth/register
- Input: { email, password }
- Output: { user, token } | { error }
- Validation: Email format, password strength

### POST /auth/login
- Input: { email, password }
- Output: { user, token } | { error }
- Rate limiting: 5 attempts per 15 minutes

## Security Considerations
- Passwords hashed with bcrypt (12 rounds)
- JWT tokens expire after 24 hours
- Account lockout after 3 failed attempts
- HTTPS required for all auth endpoints

# Implementation Tasks

## Backend Tasks
- [ ] Create User model with validation
- [ ] Implement password hashing utility
- [ ] Create user registration endpoint
- [ ] Add email uniqueness validation
- [ ] Implement login endpoint with rate limiting
- [ ] Create JWT token generation/validation
- [ ] Add account lockout mechanism
- [ ] Write unit tests for auth service

## Frontend Tasks  
- [ ] Create registration form component
- [ ] Add form validation (email, password strength)
- [ ] Implement login form component
- [ ] Add error message display
- [ ] Create protected route wrapper
- [ ] Implement logout functionality
- [ ] Add loading states for auth actions
- [ ] Write component tests

## Integration Tasks
- [ ] Set up API client for auth endpoints
- [ ] Implement token storage (localStorage/cookies)
- [ ] Add automatic token refresh
- [ ] Create auth context/state management
- [ ] Test complete auth flow
- [ ] Add error boundary for auth failures

## Documentation Tasks
- [ ] Update API documentation
- [ ] Create user guide for auth features
- [ ] Document security considerations
- [ ] Add troubleshooting guide