title: What is "pass-through authentication" in IIS 7?
body: <p>In IIS 7, after I specify the physical path for my website and click the "Test Settings" button, I get the following warning:</p>
  
  <blockquote>
    <p>The server is configured to use pass-through authentication with a built-in account to access the specified physical path. However, IIS Manager cannot verify whether the built-in account has access. Make sure that the application pool identity has Read access to the physical path. If this server is joined to a domain, and the application pool identity is NetworkService or LocalSystem, verify that<code>&lt;domain&gt;\&lt;computer_name&gt;$</code>has read access to the physical path. Then test these settings again.</p>
  </blockquote>
  
  <p>So what is pass-through authentication? Literally, it should be pass some A through some B? So what are the A and B?</p>
  
  <p>Also, I am actually using the built-in <em>ApplicationPoolIdentity</em>. Why can't IIS verify that this account has proper access rights to the physical path? Why do I need to verify it myself?</p>