Impersonation in ASP.NET Core

A colleague reached out to me with a specific scenario he had to tackle. He had an IIS hosted ASP.NET Core application using Windows Authentication where he had to execute a specific action on behalf of the current user. The typical way to do this is through impersonation. In this post I’ll explain what impersonation is and how you can get this working in ASP.NET Core.

What is impersonation?

Impersonation is a security feature that allows an application to execute code under the context of a different user identity. This capability is often used when an application needs to access resources, such as files, databases, or network services, with permissions different from those of the current user or the application's process.

By using impersonation the application temporarily assumes the identity of another user to perform specific actions, reverting back to its original identity afterward.

Some common use cases for impersonation are:

• Accessing network shares or file systems with restricted permissions.

• Performing administrative tasks that require elevated privileges.

• Connecting to databases using Windows Authentication.

Impersonation in ASP.NET Core

In classic ASP.NET, impersonation could be enabled through the web.config file. However, ASP.NET Core does not support this configuration-based impersonation. Instead, impersonation must be handled programmatically using the use WindowsIdentity.RunImpersonated or RunImpersonatedAsync.

Here’s a basic example demonstrating how to implement impersonation in an ASP.NET Core application:

	app.Run(async (context) =>
	{
	var user = (WindowsIdentity)context.User.Identity!;
	await WindowsIdentity.RunImpersonatedAsync(user.AccessToken, async () =>
	{
	//Add your code here
	});
	});

view raw Impersonate.cs hosted with ❤ by GitHub

Remark: In the example above we are using middleware to run our impersonated code but you can also use an action filter if you want(Let me know if I should add an example).

Make sure that when trying the code above that you have the following configuration set in IIS:

• Enable Windows Authentication in IIS Manager.

• Disable Anonymous Authentication if not required.

• Ensure the application pool identity has the necessary permissions for delegation if needed.

More information

Configure Windows Authentication in ASP.NET Core | Microsoft Learn