''MS-ASPNETCORE-TOKEN' does not match the expected pairing token' when calling deployed .net core API on IIS

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06-10-2024

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"MS-ASPNETCORE-TOKEN" Mismatch: Troubleshooting Your Deployed .NET Core API on IIS

The Problem

You've diligently built your .NET Core API, tested it locally, and successfully deployed it to IIS. But when you try to access it from your application, you're met with a cryptic error message: "MS-ASPNETCORE-TOKEN' does not match the expected pairing token." This error indicates that the IIS configuration is not correctly communicating with your .NET Core application, preventing it from receiving the necessary authentication information.

Scenario and Code Example

Let's imagine you have a simple .NET Core API that uses the [Authorize] attribute to secure its endpoints. This is a typical scenario:

// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthentication(JwtBearerDefaults.AuthenticationScheme)
        .AddJwtBearer(options =>
        {
            options.Authority = "https://your-identity-server.com";
            options.Audience = "your-api-audience";
        });
    services.AddAuthorization();
    // ... other services
}

// MyController.cs
[Authorize]
public class MyController : ControllerBase
{
    // ... API endpoints
}

You've deployed this API to IIS, configured your web.config, and everything seems to be in place. However, upon making a request to your API, you encounter the "MS-ASPNETCORE-TOKEN" mismatch error.

Understanding the Issue

The root cause of this error lies in the interaction between IIS and your .NET Core application. When you deploy your .NET Core application to IIS, you're essentially running it within the IIS process. IIS acts as a reverse proxy, forwarding requests to your application.

The "MS-ASPNETCORE-TOKEN" is a key part of this communication. IIS generates this token and passes it to your .NET Core application during startup to establish a secure connection.

If this token doesn't match the expected pairing token within your .NET Core application, it signifies that IIS and your application are not communicating properly. This could be due to several reasons:

• Inconsistent Configuration: The web.config file within your IIS application pool might have incorrect or missing configuration settings.
• Outdated Dependencies: The versions of your .NET Core runtime, ASP.NET Core, and related packages might be incompatible.
• Security Restrictions: IIS might be enforcing security restrictions that prevent the necessary communication between IIS and your .NET Core application.
• IIS Process Issues: The IIS process itself could be experiencing problems that hinder the communication.

Solutions and Troubleshooting

1. Verify web.config Configuration:

   • ASP.NET Core Module Version: Ensure that the aspNetCore section in your web.config file specifies the correct version of the ASP.NET Core Module. Refer to the official documentation for the appropriate version based on your .NET Core runtime.
   • Process Path: Verify that the processPath attribute within the aspNetCore section points to the correct location of your application's executable. This should typically be the dotnet executable followed by the path to your application's dll.
   • Hosting Model: Double-check that you're using the correct hosting model (InProcess or OutOfProcess) in the web.config. InProcess is the default, and usually, the best option for better performance.

2. Check for Version Compatibility:

   • .NET Core Runtime: Make sure you're using the same .NET Core runtime version both locally and in your IIS deployment.
   • ASP.NET Core Dependencies: Ensure that all your ASP.NET Core packages are compatible with the deployed .NET Core runtime.
   • IIS Modules: Verify that you have the necessary IIS modules installed, specifically the ASP.NET Core Module, which enables the communication between IIS and your .NET Core application.

3. Examine IIS Security Settings:

   • Application Pool Identity: Ensure that the application pool's identity has the necessary permissions to access the files and resources required by your .NET Core application.
   • Firewall: Confirm that your firewall rules allow communication between IIS and your .NET Core application.

4. Investigate IIS Process:

   • Restart IIS: Restarting IIS can resolve temporary problems.
   • Event Viewer: Check the Event Viewer for any error messages related to IIS or your application pool.
   • IIS Logs: Review the IIS logs for detailed information about the error and any relevant requests.

Additional Tips

• Enable Detailed Error Logging: Enable detailed error logging in your .NET Core application to provide more specific information about the "MS-ASPNETCORE-TOKEN" mismatch error.
• Use Process Monitor: The Process Monitor tool can help you analyze the communication between IIS and your .NET Core application, identifying any potential access or permission issues.
• Consider a Different Hosting Model: If the "MS-ASPNETCORE-TOKEN" mismatch issue persists despite troubleshooting, you might want to consider switching to a different hosting model, such as self-hosting or using a cloud platform like Azure App Service.

Conclusion

The "MS-ASPNETCORE-TOKEN" mismatch error can be frustrating, but by understanding the interaction between IIS and your .NET Core application, you can effectively diagnose and resolve the issue. Carefully reviewing your configuration settings, ensuring version compatibility, and examining IIS security settings are crucial steps in troubleshooting this error. Remember to consult the official ASP.NET Core documentation and community resources for further guidance and support.