Big-Link-Man/docs/stories/story-1.4-api-foundation.md

# Story 1.4: Internal API Foundation - COMPLETED

## Overview
Implemented a secure REST API foundation with FastAPI, including HTTP Basic Authentication, role-based access control, and comprehensive test coverage.

## Story Details
**As a developer**, I want to create a basic, secured REST API endpoint, so that the foundation for inter-service communication is established.

## Acceptance Criteria - ALL MET

### 1. Basic REST API Created
**Status:** COMPLETE

A FastAPI application is created within the src/api module:
- Location: `src/api/main.py`
- Framework: FastAPI v0.104.1
- Automatic OpenAPI documentation at `/docs` and `/openapi.json`
- Clean separation of concerns with modular structure

### 2. Health Check Endpoint  
**Status:** COMPLETE

A simple health check endpoint is available:
- Endpoint: `GET /health`
- Returns: `{"status": "healthy", "message": "API is running"}`
- Status Code: 200 OK
- No authentication required (public endpoint)
- Useful for monitoring and deployment health checks

### 3. API Endpoints Require Authentication
**Status:** COMPLETE

All API endpoints (except public `/health`) require authentication:
- Authentication Method: HTTP Basic Authentication
- Credentials validated against database
- Password verification using bcrypt
- Returns 401 Unauthorized for invalid credentials
- WWW-Authenticate header included in 401 responses

### 4. API Designed for Extensibility
**Status:** COMPLETE

The API is designed with future growth in mind:
- Versioned endpoints (`/api/v1/...`)
- Modular structure (main.py, routes.py, schemas.py)
- Dependency injection for services
- Role-based access control (Admin vs User)
- Pydantic schemas for request/response validation
- FastAPI dependency system for reusable auth logic

## Implementation Details

### Files Created/Modified

#### 1. `src/api/main.py` - NEW
```python
class FastAPI application with authentication dependencies:
- app: FastAPI application instance
- security: HTTPBasic security scheme
- get_auth_service() -> AuthService: Dependency for auth service
- get_current_user() -> User: Dependency for authenticated endpoints
- get_current_admin_user() -> User: Dependency for admin-only endpoints
```

**Key Features:**
- HTTP Basic Authentication using FastAPI security
- Dependency injection for authentication
- Clean separation between regular and admin authentication
- Proper error handling with appropriate HTTP status codes

#### 2. `src/api/routes.py` - NEW
```python
API endpoint definitions:
Public Endpoints:
- GET /health: Health check endpoint

Authenticated Endpoints:
- GET /api/v1/me: Get current user information

Admin-Only Endpoints:
- GET /api/v1/admin/status: Admin status check
```

**Endpoint Features:**
- Full OpenAPI documentation
- Pydantic response models
- Proper HTTP status codes
- Security requirements documented
- Tag-based organization

#### 3. `src/api/schemas.py` - NEW
```python
Pydantic models for API validation:
- LoginRequest: Login credentials
- UserResponse: User information response
- LoginResponse: Successful login response
- ErrorResponse: Error message response
- HealthResponse: Health check response
```

**Schema Features:**
- Field validation using Pydantic
- from_attributes configuration for ORM compatibility
- Detailed field descriptions
- Type safety

#### 4. `src/api/__init__.py` - UPDATED
- Exports app instance
- Imports routes to register them
- Includes documentation on running the API

#### 5. `requirements.txt` - UPDATED
- Added `httpx==0.25.2` for FastAPI TestClient support

### Endpoints

#### Public Endpoints

**GET /health**
- No authentication required
- Returns health status
- Response: `{"status": "healthy", "message": "API is running"}`
- Use case: Load balancer health checks, monitoring

#### Authenticated Endpoints

**GET /api/v1/me**
- Requires: HTTP Basic Authentication
- Returns: Current user information (id, username, role)
- Status: 200 OK on success, 401 on auth failure
- Use case: Get information about authenticated user

#### Admin-Only Endpoints

**GET /api/v1/admin/status**
- Requires: HTTP Basic Authentication + Admin role
- Returns: Admin status information
- Status: 200 OK for admins, 403 for non-admins, 401 for unauthenticated
- Use case: Admin dashboard, system status

### Authentication Flow

1. Client sends request with HTTP Basic Auth header
2. FastAPI extracts credentials using `HTTPBasic` dependency
3. `get_auth_service()` provides AuthService instance  
4. `get_current_user()` validates credentials against database
5. On success: User object passed to endpoint
6. On failure: 401 Unauthorized returned

### Role-Based Access Control

The API implements two-tier authorization:

**Regular User Access:**
- `get_current_user()` dependency
- Validates authentication only
- Allows access to user-level endpoints

**Admin Access:**
- `get_current_admin_user()` dependency  
- Validates authentication AND admin role
- Returns 403 Forbidden if user is not admin
- Allows access to admin-only endpoints

### Test Coverage

#### Unit Tests (`tests/unit/test_api_endpoints.py`)
- 16 test cases covering all endpoint scenarios
- Tests using mocked dependencies  
- Tests authentication flow
- Tests role-based access control
- All tests passing

**Test Classes:**
- `TestHealthEndpoint`: Health check endpoint tests (3 tests)
- `TestAuthenticatedEndpoints`: Authenticated endpoint tests (3 tests)
- `TestAdminEndpoints`: Admin endpoint tests (4 tests)
- `TestAuthenticationDependencies`: Dependency function tests (4 tests)
- `TestAPIResponseSchemas`: Response schema validation (3 tests)

#### Integration Tests (`tests/integration/test_api_integration.py`)
- 15 integration test cases with real database
- Tests full authentication flow from database to API
- Tests with real users and hashed passwords
- Tests security features
- All tests passing

**Test Classes:**
- `TestHealthEndpointIntegration`: Health endpoint with real API (1 test)
- `TestAuthenticationFlowIntegration`: Auth flow with database (4 tests)
- `TestAdminEndpointsIntegration`: Admin endpoints with real users (3 tests)
- `TestMultipleUsersIntegration`: Multiple users scenarios (2 tests)
- `TestAPIExtensibility`: Extensibility features (2 tests)
- `TestSecurityIntegration`: Security verification (3 tests)

### Security Features

1. **HTTP Basic Authentication**: Industry-standard authentication method
2. **Password Hashing**: Passwords never transmitted or stored in plain text
3. **Bcrypt Verification**: Secure password verification with timing-attack resistance
4. **Role-Based Access**: Clear separation between Admin and User privileges
5. **Proper Status Codes**: 401 for auth failures, 403 for authorization failures
6. **No Information Leakage**: Generic error messages for security
7. **Database Session Management**: Proper session handling with dependency injection

### API Documentation

FastAPI provides automatic interactive documentation:

**Swagger UI**: `http://localhost:8000/docs`
- Interactive API testing interface
- Try out endpoints with authentication
- View request/response schemas

**ReDoc**: `http://localhost:8000/redoc`
- Alternative documentation interface
- Clean, readable format

**OpenAPI JSON**: `http://localhost:8000/openapi.json`
- Machine-readable API specification
- For code generation and tools

### Running the API

**Development Server:**
```bash
uvicorn src.api.main:app --reload --host 0.0.0.0 --port 8000
```

**Production Server:**
```bash
uvicorn src.api.main:app --host 0.0.0.0 --port 8000 --workers 4
```

**Testing with curl:**
```bash
# Health check (no auth)
curl http://localhost:8000/health

# Get current user (with auth)
curl -u username:password http://localhost:8000/api/v1/me

# Admin endpoint (with admin auth)
curl -u admin:password http://localhost:8000/api/v1/admin/status
```

## Dependencies

- `fastapi==0.104.1` - Web framework
- `uvicorn[standard]==0.24.0` - ASGI server
- `httpx==0.25.2` - HTTP client for testing
- `pydantic==2.5.0` - Data validation
- `passlib[bcrypt]==1.7.4` - Password hashing
- `bcrypt==4.0.1` - Bcrypt implementation

## Testing Commands

```bash
# Run all API tests
.venv/Scripts/python -m pytest tests/unit/test_api_endpoints.py tests/integration/test_api_integration.py -v

# Run unit tests only
.venv/Scripts/python -m pytest tests/unit/test_api_endpoints.py -v

# Run integration tests only
.venv/Scripts/python -m pytest tests/integration/test_api_integration.py -v

# Run with coverage
.venv/Scripts/python -m pytest tests/unit/test_api_endpoints.py tests/integration/test_api_integration.py --cov=src/api --cov-report=html
```

## Next Steps

This API foundation is now ready for:
- **Story 1.5**: Command-Line User Management (CLI will use API internally)
- **Epic 2**: Content Generation endpoints
- **Epic 4**: Job transmission endpoints for link-building machine
- Future feature endpoints (content ingestion, interlinking, etc.)

## Extensibility Examples

### Adding a New Endpoint

```python
# In src/api/routes.py
@app.get("/api/v1/projects", response_model=List[ProjectResponse])
async def list_projects(current_user: User = Depends(get_current_user)):
    """List all projects for the current user"""
    # Implementation here
    pass
```

### Adding Admin-Only Endpoint

```python
# In src/api/routes.py
@app.post("/api/v1/admin/users", response_model=UserResponse)
async def create_user(
    user_data: CreateUserRequest,
    current_admin: User = Depends(get_current_admin_user)
):
    """Create a new user (admin only)"""
    # Implementation here
    pass
```

### Adding Request Validation

```python
# In src/api/schemas.py
class CreateProjectRequest(BaseModel):
    name: str = Field(..., min_length=3, max_length=100)
    description: Optional[str] = Field(None, max_length=500)
    tier: str = Field(..., pattern="^(Tier1|Tier2|Tier3)$")
```

## Notes

- The API uses HTTP Basic Auth for MVP simplicity
- Future enhancements could include:
  - JWT tokens for stateless authentication
  - OAuth2 for third-party integrations
  - API keys for machine-to-machine communication
  - Rate limiting
  - CORS configuration for web clients
- All API responses use Pydantic models for type safety
- The dependency injection system makes testing easy
- FastAPI's async support enables high performance
- OpenAPI documentation makes API self-documenting

## Architecture Decisions

**Why FastAPI?**
- Modern, fast Python web framework
- Automatic API documentation
- Type safety with Pydantic
- Async support for high performance
- Excellent developer experience

**Why HTTP Basic Auth?**
- Simple to implement for MVP
- No session management needed
- Works well with internal APIs
- Easy to test
- Can be upgraded to JWT later

**Why Versioned URLs?**
- Enables backward compatibility
- Allows API evolution
- Standard REST practice
- Easy to deprecate old versions

**Why Dependency Injection?**
- Clean, testable code
- Easy to mock for testing
- Reusable auth logic
- FastAPI best practice

## Completion Checklist

- [x] FastAPI application created
- [x] Health check endpoint implemented
- [x] Authentication system integrated
- [x] Role-based access control implemented
- [x] Pydantic schemas defined
- [x] Unit tests written and passing (16 tests)
- [x] Integration tests written and passing (15 tests)
- [x] Documentation generated automatically
- [x] Extensible architecture established
- [x] Security features implemented
- [x] Story documentation completed