Скачать или смотреть Solving Bearer Authentication Issues in ASP.NET Core with Flutter Clients

Discover how to fix the `404 error` when using Bearer Authentication in ASP.NET Core API with Flutter applications, and learn the key differences between Cookie and Bearer Authentication.
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This video is based on the question https://stackoverflow.com/q/63586339/ asked by the user 'Nikita Belov' ( https://stackoverflow.com/u/4618228/ ) and on the answer https://stackoverflow.com/a/63600668/ provided by the user 'Nikita Belov' ( https://stackoverflow.com/u/4618228/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Troubleshooting Bearer Authentication in ASP.NET Core with Flutter Clients

When working with ASP.NET Core and a Flutter client, developers often encounter various challenges related to authentication methods. One common issue arises when implementing Bearer Authentication, leading to unexpected "404 Not Found" errors despite successfully receiving responses when testing requests through tools like Postman. In this guide, we'll explore a specific problem you might face, the reason behind it, and provide a clear solution to ensure your Flutter application communicates with the ASP.NET Core backend seamlessly.

The Problem

A developer configured a Web API project using ASP.NET Core 3.1 and set up Bearer Authentication as follows:

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

They added the [Authorize] attribute in the API controller and called app.UseAuthorization(); in the Configure method. Testing through Postman yielded correct responses, but sending a request from the Flutter app resulted in a "404 Not Found" error. The request from Flutter was structured as follows:

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

Why the Confusion?

The discrepancy arises due to different authentication methods being used between the app and the server. While Postman can handle Cookies more adeptly, Flutter's direct header inclusion for Bearer tokens led to a failure in authentication with a "404 Not Found" response.

The Solution

The root of the issue is that the controller was still utilizing cookie-based authentication rather than switching to Bearer tokens specifically. To resolve this problem, the developer should replace the [Authorize] attribute with a parameter specifying the correct authentication scheme:

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

Step-by-Step Adjustment

Update the Controller: Modify the [Authorize] attribute in your controller to specify the authentication scheme:

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

Test Again: After updating the attribute, test your Flutter application once more, ensuring that your Bearer token is still valid.

Inspect Headers: Make sure that the Authorization header is correctly set in the requests generated by your Flutter application.

Why Postman Worked but Flutter Failed?

Postman has a unique advantage when it comes to handling cookie-based authentication because it automatically manages cookies between requests. When the user signed in using Postman, it would capture the .AspNetCore.Identity.Application cookie and use it for subsequent requests. In contrast, the Flutter client didn't manage session cookies, and thus, it didn't authenticate correctly without the proper bearer configuration.

Conclusion

Encountering a "404 Not Found" error when using Bearer Authentication in ASP.NET Core with a Flutter client may stem from confusion around the authentication method that the API expects. By ensuring your controller explicitly utilizes JwtBearerDefaults.AuthenticationScheme, you can easily resolve the issue and facilitate proper communication between the Flutter app and your ASP.NET Core Web API.

In summary, while tools like Postman may simplify the testing process, it's vital to understand how your authentication method interacts with your codebase for it to function correctly in production environments. Happy coding!