Скачать или смотреть Solving the Redirect_URI Issue in ASP.NET Core with Azure AD Behind a Reverse Proxy

Learn how to configure your ASP.NET Core app to handle the correct `redirect_uri` when using Azure AD authentication behind a reverse proxy like Azure Application Gateway.
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Handling Redirect_URI Issues with ASP.NET Core and Azure AD When Using a Reverse Proxy

When working with web applications, especially those utilizing Azure AD authentication, you may encounter a frustrating issue: the redirect_uri is set incorrectly during the authentication flow. If your application is hosted on an Azure App Service and is using Azure Application Gateway as a reverse proxy, you might notice that upon successful authentication, the redirect is pointing to *.azurewebsites.net instead of your configured custom domain, *.mydomain.com. This post aims to provide a comprehensive solution to this common problem.

Understanding the Problem

The Setup

You have an ASP.NET Core 3.1 application set up with Azure AD authentication, utilizing forwarded headers. The basic operations involve:

ASP.NET Core configured for Azure AD.

An Azure Application Gateway acting as a reverse proxy.

Forwarded headers to capture the original request details.

The Issue

The core issue arises during the authentication flow. Instead of redirecting users to your intended domain after they sign in, they are redirected to the default Azure App Service domain. The headers involved in this issue include:

X-FORWARDED-PROTO

X-FORWARDED-PORT

X-ORIGINAL-HOST

Of these, X-ORIGINAL-HOST seems to correctly reflect your domain. The question becomes, how can you inform your ASP.NET Core application to use these headers correctly?

Step-by-Step Solution

Adjusting Your Application Configuration

To resolve the redirect_uri issue, here’s what you need to do:

Modify HTTP Settings:

Navigate to the HTTP settings of your Azure Application Gateway.

Under Hostname settings, specify your custom domain (e.g., *.mydomain.com).

This is crucial as it dictates how requests are passed to your backend application.

Configure Azure AD Settings:
Ensure that the Azure AD registration for your application reflects the custom domain as the valid redirect URI. This might involve updating the application registration in the Azure portal to recognize not just the default Azure domain but also your configured custom domain.

Verifying Header Forwarding

In your ASP.NET Core app, ensure you have correctly configured forwarded headers:

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

Make sure that you're using app.UseForwardedHeaders(); in both your development and production environment settings. This ensures that ASP.NET Core is aware of how to interpret the forwarded headers:

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

Testing Your Changes

After making the above adjustments, it’s essential to thoroughly test your application. Go through the authentication process to ensure that upon successful login, the redirection occurs to your custom domain rather than the default Azure one.

Conclusion

Misconfiguration of the redirect_uri in applications secured by Azure AD is a common challenge, especially when using a reverse proxy. However, with a few strategic changes in both your Azure Application Gateway settings and your ASP.NET Core application configuration, you can ensure that the authentication flow operates seamlessly. By adjusting the hostname settings and ensuring that your application correctly interprets forwarded headers, you can easily resolve this issue.

For further reading and troubleshooting, refer to Azure documentation on managing redirects and forward headers, as well as ASP.NET Core security features.