title: context.Request.ServerVariables["LOGON_USER"] is string empty
body: <p>I am running web app on windows7 enterprise iis7.5.
  My webapp uses Windows Authentication and ASP.NET v4.0 applicationpool with <code>identity=applicationpoolIdentity</code>.</p>
  
  <p>I want to get the logon user name with <code>context.Request.ServerVariables["LOGON_USER"]</code>, but it's string is empty. Why?</p>
  
  <p>Thanks.</p>