Implement User Login

[poksyy]

1. Create a DTO (LoginRequest)
   • This DTO will handle user login requests.
   • Include necessary fields: username and password.
   • Add validation annotations like @notblank.
2. Implement Authentication in UserService
   • Inject AuthenticationManager to authenticate users.
   • Retrieve user details from the database using UserRepository.
   • Use BCryptPasswordEncoder.matches() to compare passwords.
   • Generate a JWT token if authentication is successful.
3. Modify JwtService for Token Generation
   • Add a method to generate a token upon successful login.
   • Ensure the token includes user details for authorization.
4. Build AuthController for Login
   • Create a /login endpoint in AuthController.
   • Call UserService to authenticate the user.
   • Return the generated JWT token upon successful authentication.
5. Test Login in Postman
   • Send a POST request to /api/auth/login with JSON data:
   • Verify that a JWT token is returned in the response.
   • Use the token in subsequent requests for authentication.

{
    "username": "testuser",
    "password": "password123"
}