Resolving Token Authentication Issues in ASP.NET Core API with OpenIddict for Next.js Web Apps

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The Problem: Redirection Instead of Proper Status Codes

Why Redirection Happens

The redirection occurs because ASP.NET Core’s cookie authentication handler assumes that the user is not authenticated when no valid cookie is provided. This is a common behavior seen in setups where both token and cookie authentication are used. If the token authentication fails, the framework redirects to the login page.

The Solution: Forcing Token Authentication

To overcome this issue, you need to explicitly specify the authentication scheme for your API action. By using the Authorize attribute, you can force the API to validate the bearer token. Here’s a step-by-step guide to implement this solution:

Step 1: Update your API Action

Modify your API action to specify OpenIddict's authentication scheme explicitly. This ensures your API checks for the bearer token rather than resorting to cookie authentication.

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Step 2: Ensure Middleware Configuration

Ensure that your Startup configuration is correctly set up to support token authentication. This involves making sure that both authentication and authorization middlewares are applied in the correct order, as shown below:

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

Step 3: Test the API Endpoint

Final Thoughts

Dealing with authentication in a multi-frontend environment can introduce complexities, particularly when combining traditional server-rendered pages with modern single-page applications. By ensuring that your ASP.NET Core API specifically recognizes and processes bearer tokens through explicit configurations, you can mitigate issues like unexpected redirections effectively.

The key to resolving these issues lies in understanding how different authentication schemes operate within the ASP.NET Core framework. By following the steps outlined above, you'll enhance your web application's ability to properly handle token-based authentication.