**AuthenticationCredentialsNotFoundException in Spring - A Comprehensive Guide**

As developers, we often come across various exceptions while working with different frameworks and libraries. One such exception that frequently occurs when working with Spring Security is the AuthenticationCredentialsNotFoundException. In this article, we will explore this exception in detail and understand how to handle it effectively.

Understanding AuthenticationCredentialsNotFoundException

The AuthenticationCredentialsNotFoundException is a specific exception class provided by Spring Security. It is thrown when the current authentication request does not have the required credentials for the requested operation.

In simpler terms, this exception occurs when a user tries to access a protected resource without logging in or providing valid credentials. It indicates that the user’s request cannot be authenticated, and access to the requested resource is denied.

Common Scenarios Leading to AuthenticationCredentialsNotFoundException

Let’s consider a few scenarios in which the AuthenticationCredentialsNotFoundException can be encountered:

1. Accessing Restricted Endpoints without Authentication

Suppose you have defined certain endpoints in your application that require the user to be authenticated. If a user tries to access these endpoints without logging in, Spring Security will throw the AuthenticationCredentialsNotFoundException.

@RestController
public class UserController {
    
    @GetMapping("/user/profile")
    public ResponseEntity<UserProfile> getUserProfile(Authentication authentication) {
        // retrieve user profile details for the authenticated user
        // ...
    }
    
    // other methods

}

2. Invalid Authentication Token

If you are using token-based authentication, an invalid token can also lead to the AuthenticationCredentialsNotFoundException. This can happen when the token is expired, not properly formatted, or tampered with.

@Component
public class JwtTokenProvider {

    // ...

    public Authentication getAuthentication(String token) {
        if (isValidToken(token)) {
            Claims claims = extractClaims(token);
            UserDetails userDetails = userService.loadUserByUsername(claims.getSubject());
            return new UsernamePasswordAuthenticationToken(userDetails, "", userDetails.getAuthorities());
        } else {
            throw new AuthenticationCredentialsNotFoundException("Invalid token");
        }
    }

    // ...

}

Handling AuthenticationCredentialsNotFoundException

Now that we are familiar with the scenarios leading to this exception, let’s discuss some approaches to handle it effectively.

1. Custom Exception Handling

To handle the AuthenticationCredentialsNotFoundException, we can create a global exception handler that catches and processes this exception accordingly.

@ControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(AuthenticationCredentialsNotFoundException.class)
    public ResponseEntity<ErrorResponse> handleAuthenticationCredentialsNotFoundException(AuthenticationCredentialsNotFoundException ex) {
        ErrorResponse errorResponse = new ErrorResponse(HttpStatus.UNAUTHORIZED.value(), ex.getMessage());
        return new ResponseEntity<>(errorResponse, HttpStatus.UNAUTHORIZED);
    }

}

2. Custom UserDetailsService

If you are using Spring’s UserDetailsService to load user details for authentication, make sure you handle the case where the user is not found. In such cases, you can throw the AuthenticationCredentialsNotFoundException.

@Service
public class UserDetailsServiceImpl implements UserDetailsService {

    // ...

    @Override
    public UserDetails loadUserByUsername(String username) throws UsernameNotFoundException {
        User user = userRepository.findByUsername(username)
                .orElseThrow(() -> new AuthenticationCredentialsNotFoundException("User not found"));

        // ...
    }

    // ...

}

3. Restrict Access to Endpoints

To prevent the AuthenticationCredentialsNotFoundException from occurring, you can restrict access to specific endpoints using Spring Security’s configuration. By adding the permitAll() method to the configuration, you allow unrestricted access to certain endpoints without requiring authentication.

@Configuration
@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {

    // ...

    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.authorizeRequests()
                .antMatchers("/public/**").permitAll()
                .anyRequest().authenticated();
    }

    // ...

}

Conclusion

In this comprehensive guide, we explored the AuthenticationCredentialsNotFoundException exception in Spring Security. We examined the common scenarios leading to this exception and discussed various approaches to handle it effectively. By implementing custom exception handling and ensuring proper configuration, we can provide a better user experience and enhance the security of our applications.

Remember, handling exceptions gracefully is an essential aspect of building robust and secure applications. Stay proactive and keep exploring different exception-handling techniques to make your code more resilient.

For more information, you can refer to the official Spring Security documentation on Exception Handling and Access Control.

Happy coding!