Add JWT authentication system with secure token generation and protected endpoints

[Copilot]

This PR implements a complete JWT-based authentication system as requested in the issue. The system provides secure token generation and protected endpoint access using industry-standard JWT tokens.

New Features

Authentication Endpoints

• POST /api/v1/auth/login - Login endpoint that generates JWT tokens

  • Accepts username/password credentials (admin/password123)
  • Returns JWT token with 24-hour expiration
  • Proper error handling for invalid credentials (401 Unauthorized)

• GET /api/v1/test/protected - Protected test endpoint requiring authentication

  • Requires valid Bearer token in Authorization header
  • Returns user information and timestamp
  • Demonstrates JWT middleware functionality

Security Implementation

• JWT tokens signed using HS256 algorithm
• Secure token validation middleware
• Proper error handling for missing/invalid tokens
• 24-hour token expiration for security

Example Usage

# Login to get token
curl -X POST http://localhost:3030/api/v1/auth/login \
  -H "Content-Type: application/json" \
  -d '{"username": "admin", "password": "password123"}'

# Use token to access protected endpoint
curl -X GET http://localhost:3030/api/v1/test/protected \
  -H "Authorization: Bearer <jwt_token>"

Technical Details

Dependencies Added

• jsonwebtoken - JWT token generation and validation
• chrono - Date/time handling for token expiration

New Components

• Authentication Models - LoginRequest, TokenResponse, Claims
• JWT Middleware - Token validation and extraction
• Auth Controller - Login and protected endpoint handlers
• Error Handling - Proper 401 responses for authentication failures

Documentation

• Full OpenAPI/Swagger documentation for all new endpoints
• Security schemas defined for Bearer token authentication
• Complete integration test suite (5 new tests covering all scenarios)

Testing

All existing functionality remains unchanged and tested. New comprehensive test coverage includes:

• Valid credential login
• Invalid credential rejection
• Protected endpoint access with valid token
• Proper 401 responses for missing/invalid tokens
• End-to-end authentication flow

The implementation follows the existing codebase patterns and maintains the clean architecture with proper separation of concerns.

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