Error message is not displayed when when validating a user using spring framework - spring-boot

Question

So I am trying to authenticate a user using a POST login API but the issue is when the user does not exist (meaning username (unique) not in the database) the thrown error message is not displayed on the client side (POSTMAN). I tried debugging and the error is thrown but not displayed all I see is Status: 401 Unauthorized from POSTMAN
But when the user exists but the password doesn't match, it displays the correct thrown error message. NOTE: I am using spring's OAuth 2.0 Resource Server JWT
Controller method
#PostMapping(path = "/login", consumes = "application/json")
public ResponseEntity<?> login(#Valid #RequestBody UserDTO userDTO) throws UsernameNotFoundException {
LOGGER.info("Authenticating {}", userDTO.getUsername());
userDTOService.confirmUser(userDTO); // Where the issue occurs
Authentication authentication = authenticationManager
.authenticate(new UsernamePasswordAuthenticationToken(userDTO.getUsername(), userDTO.getPassword()));
return ResponseEntity.ok()
.header(
HttpHeaders.AUTHORIZATION,
tokenService.generateToken(authentication)
)
.build();
}
Service method (confirm user method)
public void confirmUser(UserDTO userDTO) throws UsernameNotFoundException {
/*
* Check if username exist in the database
* Check if the password provided equals password in database
* */
String username = userDTO.getUsername();
String password = userDTO.getPassword();
Optional<User> user = userRepository.findUserByUserName(username);
// This error is not displayed
if (user.isEmpty()) {
LOGGER.error("User {} does not exist", username);
throw new UsernameNotFoundException(username + " does not exist");
}
boolean checkingCredentials = user
.stream()
.anyMatch(
param ->
param.getUsername().equals(username)
&&
passwordEncoder.matches(password, param.getPassword())
);
if (!checkingCredentials) {
LOGGER.error("Bad user credentials");
throw new RuntimeException("Please check username or password");
}
}

Answer 1

The reason I was getting a 401 instead of the correct error message is because my approach was wrong. I had 2 solutions to this but I am not sure if the 2nd is the industry standard.
The first approach:
Pass the user credentials to a UsernamePasswordToken to generate a token.
Then I the token into the authentication manager to be authenticated
Surround the auth manager in a try catch block to return an exception. The thrown error message will be of your chosen.
The second approach:
I want to check if user exists in the database or else throw Not found exception
If step 1 passed then I want to check the user password trying to log in and the hashed password in the database. If they do not match, I want to throw an invalid password exception
If no error is thrown, then I want to pass the users name, password and authorities into UsernamePasswordAuthenticationToken().