Solving the CORS Issue in Spring Authorization Server 0.3.1

Discover how to fix the pesky `CORS` issue when implementing a Spring Authorization Server using a step-by-step explanation that guides you through effective solutions.
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Navigating CORS Issues in Spring Authorization Server 0.3.1

When developing web applications that utilize both a frontend and a backend, one common issue that developers face is the CORS (Cross-Origin Resource Sharing) problem. This issue often arises during interactions between the client and server, especially when their origins differ. Recently, a developer encountered a CORS problem while implementing an Authorization Server using Spring Authorization Server 0.3.1, and that’s what we are going to address in this guide.

Understanding the CORS Problem

In the developer's scenario, the authorization server was correctly set up, and the Authorization Code workflow was implemented successfully. However, they experienced a frustrating 401 Unauthorized error upon reaching the final step of the workflow, along with the following error message logged in the browser console:

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This error indicates that the server is refusing the request due to cross-origin access policies. Specifically, the preflight request, which is a preliminary check made by the browser, failed because the server did not respond with the appropriate headers.

The Solution: Implementing CORS Correctly

The first step in resolving this issue is to ensure that the CORS configuration is set up correctly in the Spring application. The original CORS setup utilized CorsConfigurationSource, which can sometimes lead to complications. Instead, a more effective approach is to create a custom filter to handle CORS requests.

Step-by-Step Solution

Here’s how to resolve the CORS issue in the Spring Authorization Server:

Create a Simple CORS Filter Class:
You'll need to create a new filter class that will handle CORS requests directly. This class will manage CORS headers and preflight requests, ensuring that browsers can communicate effectively with the server.

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Remove the CorsConfigurationSource:
By implementing the SimpleCORSFilter, you no longer need the previous CorsConfigurationSource in your security filter chain bean.

Modify Security Configurations:
Ensure that your authorization server and standard security filter chains correctly permit the required requests without additional CORS handling.

Conclusion

By creating a custom CORS filter, we effectively addressed the CORS issue experienced in the Spring Authorization Server. This solution simplifies the handling of preflight requests and ensures that the appropriate headers are provided in all necessary scenarios. If you're facing similar challenges with cross-origin requests, consider implementing a custom filter as a long-term solution.

Remember: Properly configuring CORS is essential for secure and functional web applications, especially when dealing with multiple origins. If you have any further questions or need assistance, feel free to leave comments below!

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