Customize Keycloak Error Page with Spring Boot to Handle Unauthorized Access Errors

Learn how to effectively customize the error page for `Keycloak` in your `Spring Boot` application to return specific JSON error responses for unauthorized access.
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Customizing Keycloak Error Page in Spring Boot

When developing applications, handling authentication errors gracefully is crucial to providing a smooth user experience. For developers using Keycloak with Spring Boot, managing the way your application responds to authentication failures can be a bit tricky.

In this guide, we will explore how to customize the Keycloak error page within a Spring Boot application. We will address a common issue where unauthorized access returns an empty response instead of a desirable JSON error message.

Problem Overview

As a developer utilizing the keycloak-spring-boot-starter, you may find that while authentication works well, any failure to authenticate results in an empty response. You might have tried implementing solutions such as:

Using -ExceptionHandler

Implementing an ErrorController

Creating an ErrorViewResolver

Modifying error pages via WebServerCustomizer

However, these attempts may not yield the desired results, leaving you in a rut. The ultimate goal is to provide a JSON error response that aligns with the rest of your application's error handling.

Proposed Solution

Fortunately, there exists a way to manage this effectively with the current versions of spring-security-web (5.4+). Below is a straightforward approach that can be implemented in your Spring Boot application.

Create a Custom RequestRejectedHandler

One effective method is to implement a custom RequestRejectedHandler. This handler will intercept requests that result in a RequestRejectedException, allowing you to define how your application should respond.

Example Code

Here’s an example of how to create a custom FirewallRequestRejectedHandler:

[[See Video to Reveal this Text or Code Snippet]]

How It Works

Handle Requests: Whenever a request is rejected due to authentication failure, this custom handler will take over.

Logging: You can log the request rejection for debugging and monitoring purposes.

Set Attributes: The exception from the request is set as an attribute accessible to the ErrorController.

Send Error Response: Finally, a JSON response with a 401 error code and a message like "Access denied" is sent to the client.

Conclusion

With this setup, you can maintain a consistent error handling mechanism across your Spring Boot application. Instead of returning an empty response when authentication fails, you'll provide a clear and informative JSON error message.

This approach enhances the user experience while also adhering to RESTful best practices. Now, your application can effectively inform users of unauthorized access attempts while seamlessly integrating the necessary authentication mechanisms provided by Keycloak.

By implementing a RequestRejectedHandler, you have successfully taken a step forward in customizing Keycloak’s error handling in a Spring Boot environment. Enjoy crafting delightful user experiences with your enhanced error responses!

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