Solving the invalid_token Error in JWT Bearer Token Authentication

Описание: Learn how to troubleshoot and fix the 'invalid_token' error in JWT authentication with Azure Active Directory. This guide provides clear steps and code snippets to ensure seamless integration between your client and server applications.
---
This video is based on the question https://stackoverflow.com/q/75936887/ asked by the user 'MChak' ( https://stackoverflow.com/u/10972220/ ) and on the answer https://stackoverflow.com/a/75937202/ provided by the user 'Tore Nestenius' ( https://stackoverflow.com/u/68490/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Jwt bearer token audience invalid even though correct audience is in token

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the invalid_token Error in JWT Authentication

Setting up JWT token authentication can sometimes be a daunting task, especially when we encounter errors that seem perplexing. One common issue developers may face is the 401 Unauthorized error, which often comes with a message indicating an "invalid token." This situation arises particularly when the audience claim in the token does not match the expected audience on the server side. In this guide, we will explore a specific scenario where this problem occurs and how we can resolve it.

The Scenario

Imagine you have a local server application named demoServer intended to authenticate users through an access token received from a client application called demoClient. Your environment is set up with the following components:

demoServer: An ASP.NET Core Web API hosted locally.

demoClient: A WPF application that allows users to log in and retrieves an access token from Azure Active Directory (AAD).

Azure AD: Here, both applications are registered, enabling smooth token generation and verification.

Following the necessary steps, you've successfully implemented the login mechanics through the Microsoft login interface and are able to obtain an access token. However, when you attempt to use this token to call your server, it returns a 401 Unauthorized error along with details mentioning an invalid audience. This can be frustrating, especially when the audience claim (aud) in your decoded JWT token seems to match.

Diagnosing the Problem

After examining the configuration in your demoServer, you may have noticed lines like this in your program.cs:

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

You might have decoded the JWT token and confirmed that the aud claim does indeed contain the value demoServer-applicationId-inAzureAAD. Yet, you're still facing that dreaded invalid token error.

The Solution

The resolution to this problem lies in correcting the options.Audience assignment in your server application. Instead of including the prefix api:// with the audience ID, you should assign it as follows:

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

This simple change should resolve the 401 Unauthorized error you are experiencing because the expected audience in your server's configuration must exactly match the audience claim provided in your JWT token.

Steps to Implement the Solution

Edit the audience configuration: Go to your program.cs file in the demoServer application and change the audience assignment as shown above.

Restart your server application: Ensure that the changes take effect by restarting the server.

Test authentication: Try logging in through the demoClient again, and send the access token to the server. Check if you can make successful API requests without encountering a 401 Unauthorized error.

Conclusion

Experiencing authentication errors can be disheartening, especially when you're confident that everything else has been configured correctly. By focusing on the audience configuration in your JWT authentication setup, you can eliminate the common invalid_token error. This solution not only enhances your understanding of JWT but also strengthens the integration between your client and server applications.

If you continue facing issues even after this adjustment, consider revisiting both your app registrations in Azure AD and the token claims to ensure everything aligns perfectly. Happy coding!