DeutschLernen/docs/features/user-authentication.md

# Feature: User Authentication & Authorization

> **Status**: ⏳ Planned  
> **Priority**: High  
> **Complexity**: Medium  
> **Estimate**: 4-6 hours  
> **Assignee**: -  
> **Created**: May 31, 2025  
> **Target Completion**: -  
> **PR**: -  
> **Related Features**: Infrastructure Setup, Lesson Management

---

## 📌 Overview

### Purpose
Implement user authentication and authorization system using ASP.NET Core Identity with JWT token-based authentication.

### User Story
As a user, I want to register, login, and access my personalized learning content so that I can track my progress and continue from where I left off.

### Acceptance Criteria
- [ ] Users can register with username, email, and password
- [ ] Users can login with email and password
- [ ] Users receive JWT token upon successful authentication
- [ ] JWT token is required for protected API endpoints
- [ ] Token expiration and refresh mechanism
- [ ] Password hashing for security
- [ ] Current user information available via /api/auth/me

---

## 📋 Requirements

### Functional Requirements
| ID | Requirement | Priority |
|----|-------------|----------|
| FR-001 | User registration endpoint | High |
| FR-002 | User login endpoint | High |
| FR-003 | JWT token generation and validation | High |
| FR-004 | Protected routes require authentication | High |
| FR-005 | Current user endpoint | Medium |
| FR-006 | Password reset functionality | Low |
| FR-007 | Email verification (optional for MVP) | Low |

### Non-Functional Requirements
- Security: Passwords hashed with bcrypt or similar
- Security: JWT tokens expire after 24 hours
- Security: Refresh tokens for seamless UX
- Performance: Authentication < 500ms
- Compatibility: Works with React frontend

---

## 🏗️ Technical Design

### Components Involved
- **Backend**: AuthController, AuthService, JWT configuration
- **Database**: Users table (from initial schema)
- **Models**: User, LoginDto, RegisterDto, AuthResponse
- **Middleware**: JWT authentication middleware

### Data Flow
```
User Registration:
1. Frontend POST /api/auth/register with {username, email, password}
2. Backend validates input
3. Backend hashes password
4. Backend creates user in database
5. Backend generates JWT token
6. Returns {userId, token} to frontend

User Login:
1. Frontend POST /api/auth/login with {email, password}
2. Backend validates credentials
3. Backend generates JWT token
4. Returns {userId, token} to frontend

Protected Endpoint:
1. Frontend includes token in Authorization header
2. Backend middleware validates token
3. Backend processes request if valid
4. Returns 401 if token invalid/expired
```

### API Endpoints
| Endpoint | Method | Description | Auth Required |
|----------|--------|-------------|----------------|
| `/api/auth/register` | POST | Register new user | No |
| `/api/auth/login` | POST | Login existing user | No |
| `/api/auth/me` | GET | Get current user info | Yes |
| `/api/auth/logout` | POST | Invalidate token | Yes |
| `/api/auth/refresh` | POST | Refresh expired token | Yes |

### Database Schema (from application-plan.md)
```sql
CREATE TABLE Users (
    Id SERIAL PRIMARY KEY,
    Username VARCHAR(50) UNIQUE NOT NULL,
    Email VARCHAR(100) UNIQUE NOT NULL,
    PasswordHash VARCHAR(255) NOT NULL,
    CurrentLevel VARCHAR(10) DEFAULT 'A1',
    Streak INT DEFAULT 0,
    TotalPoints INT DEFAULT 0,
    CreatedAt TIMESTAMP DEFAULT NOW()
);
```

---

## 🚀 Implementation Plan

### Phase 1: Backend Authentication (3-4 hours)
- [ ] Create User model and DTOs (RegisterDto, LoginDto, AuthResponse)
- [ ] Configure ASP.NET Core Identity
- [ ] Create AuthService with user registration logic
- [ ] Create AuthService with user login logic
- [ ] Configure JWT token generation
- [ ] Create AuthController with endpoints
- [ ] Add JWT authentication middleware
- [ ] Configure CORS for frontend

### Phase 2: Database Integration (1-2 hours)
- [ ] Update User entity to match schema
- [ ] Configure EF Core user repository
- [ ] Implement password hashing
- [ ] Create user seed data (admin user)
- [ ] Test database operations

### Phase 3: Token Management (1 hour)
- [ ] Configure JWT settings in appsettings.json
- [ ] Implement token validation middleware
- [ ] Add token refresh mechanism
- [ ] Set up token expiration (24 hours)
- [ ] Configure refresh token rotation

### Phase 4: Frontend Integration (Optional - if doing full stack)
- [ ] Create auth service in React
- [ ] Implement login/registration forms
- [ ] Store token in localStorage/cookies
- [ ] Add auth headers to API requests
- [ ] Handle token expiration

### Milestones
| Milestone | Date | Status |
|-----------|------|--------|
| Backend Auth Complete | - | ⏳ |
| Database Integration | - | ⏳ |
| Token Management | - | ⏳ |
| Frontend Integration | - | ⏳ |

---

## ✅ Tasks

### Backend
- [ ] Create Models/User.cs with properties
- [ ] Create DTOs/Auth/RegisterDto.cs
- [ ] Create DTOs/Auth/LoginDto.cs
- [ ] Create DTOs/Auth/AuthResponse.cs
- [ ] Create Services/AuthService.cs
- [ ] Create Controllers/AuthController.cs
- [ ] Configure JWT in Program.cs
- [ ] Add [Authorize] attribute to protected endpoints
- [ ] Create AuthMiddleware.cs
- [ ] Configure CORS policy
- [ ] Write unit tests for AuthService
- [ ] Write integration tests for AuthController

### Database
- [ ] Update User entity mapping
- [ ] Create UserRepository
- [ ] Implement password hashing
- [ ] Create migration for Users table
- [ ] Seed admin user

### Token Management
- [ ] Configure JWT settings
- [ ] Implement token generation
- [ ] Implement token validation
- [ ] Implement token refresh
- [ ] Set token expiration

### Frontend (Optional)
- [ ] Create authService.ts
- [ ] Create LoginPage component
- [ ] Create RegisterPage component
- [ ] Create AuthContext for user state
- [ ] Implement protected route wrapper
- [ ] Add logout functionality

---

## 🔗 Dependencies

### Feature Dependencies
- [Infrastructure Setup](infrastructure-setup.md) - Required (backend project and database)

### Technical Dependencies
- ASP.NET Core Identity
- JWT Bearer Authentication package
- BouncyCastle or similar for password hashing

### Blockers
- [ ] Infrastructure Setup must be complete first

---

## ✅ Definition of Done

### General Criteria (All Features)
- [ ] All acceptance criteria met and verified
- [ ] All tasks in this document completed
- [ ] Code follows Clean Architecture principles
- [ ] Code reviewed and approved by at least 1 team member
- [ ] All tests passing (unit, integration)
- [ ] Documentation updated (README, AGENTS.md if applicable)
- [ ] Feature works in development environment
- [ ] Feature deployed to staging environment
- [ ] Performance meets defined targets
- [ ] Security review completed
- [ ] No critical bugs or blockers

### Authentication-Specific Criteria
- [ ] Users can successfully register with valid credentials
- [ ] Users can successfully login with valid credentials
- [ ] Invalid credentials are rejected with appropriate error messages
- [ ] JWT tokens are generated and validated correctly
- [ ] Token expiration works as configured
- [ ] Token refresh mechanism works
- [ ] Protected endpoints reject requests without valid tokens
- [ ] Passwords are hashed and never stored in plain text
- [ ] Rate limiting on auth endpoints configured

---

## 🧪 Testing Strategy

### Testing Approach

| Test Type | Coverage | Tools | Responsibility |
|-----------|----------|-------|----------------|
| Unit Tests | 80%+ code coverage | MsTest, Moq | Backend Dev |
| Integration Tests | All service interactions | MsTest, TestContainers | Backend Dev |
| API Tests | All endpoints | MsTest, HttpClient | Backend Dev |
| Frontend Unit Tests | Component logic | Vitest | Frontend Dev |
| Frontend Integration | Service integration | Vitest | Frontend Dev |
| E2E Tests | Critical user journeys | Playwright | QA/Dev |
| Manual Testing | Exploratory, edge cases | BrowserStack | QA |

### Authentication-Specific Tests

#### Backend Tests
- [ ] Register with valid data → success
- [ ] Register with duplicate email → error
- [ ] Register with duplicate username → error
- [ ] Register with invalid password → error
- [ ] Login with valid credentials → success
- [ ] Login with invalid email → error
- [ ] Login with invalid password → error
- [ ] Login with valid token → success
- [ ] Login with expired token → error
- [ ] Login with invalid token → error
- [ ] Access protected endpoint without token → 401
- [ ] Access protected endpoint with valid token → success
- [ ] Access protected endpoint with invalid token → 401
- [ ] Token refresh → new valid token
- [ ] Rate limiting on login attempts → 429 after N attempts

#### Frontend Tests
- [ ] Registration form validation
- [ ] Registration form submission
- [ ] Login form validation
- [ ] Login form submission
- [ ] Token storage in localStorage/cookies
- [ ] Token inclusion in API requests
- [ ] Protected route redirection
- [ ] Logout functionality
- [ ] Session expiration handling

---

## 📝 Notes & Decisions

### Decisions Made
| Date | Decision | Rationale |
|------|----------|-----------|
| May 31, 2025 | Use JWT over cookies | Stateless, works well with SPAs, scalable |
| May 31, 2025 | ASP.NET Core Identity | Built-in, well-tested, integrates with EF Core |
| May 31, 2025 | 24-hour token expiration | Balance between security and UX |

### Technical Notes
- Store only password hash, never plain text
- Use HttpOnly cookies for refresh tokens if possible
- Sanitize username/email inputs to prevent injection
- Rate limit login attempts to prevent brute force

### Gotchas
- ⚠️ JWT secret must be long and random (>32 characters)
- ⚠️ Token must be stored securely on frontend (HttpOnly cookie or secure localStorage)
- ⚠️ CORS must be configured to accept credentials if using cookies
- ⚠️ Password hashing should use work factor appropriate for your hardware

---

## 📊 Progress History

| Date | Status Change | Notes |
|------|---------------|-------|
| May 31, 2025 | Created | Initial plan based on application-plan.md |

---

## 📎 Related Files & Links

- Architecture: [Backend Structure](../architecture/backend-structure.md)
- Database Schema: [Initial Database Schema](../database/initial-database-schema.sql)
- Application Plan: [Application Plan](../architecture/application-plan.md)
- Reference: [ASP.NET Core Identity Docs](https://docs.microsoft.com/en-us/aspnet/core/security/authentication/identity)
- Reference: [JWT in .NET](https://docs.microsoft.com/en-us/aspnet/core/security/authentication/jwt/)

---

*Feature created from application-plan.md*