Elevate impersonated credentials to app pool credentials in IIS

I am using impersonation in an application in IIS. I need to write a file to the file system, but don't want to use the impersonated user's credentials in this one case. I need to use the credentials of the app pool.

How do I temporarially elevate a worker process' credentials from impersonated credentials to the app pool's credentials?

From stackoverflow

• Found the answer after much Googling.

  using System.Security.Principal;
  WindowsImpersonationContext ctx = 
        WindowsIdentity.Impersonate(System.IntPtr.Zero);
  //do stuff in app pool's security context
  ctx.Undo();
  

  http://www.mindsharpblogs.com/todd/archive/2005/05/03/467.aspx