title: Adding custom request header works for IIS 7.0 but not Asp.net dev server
body: <p>We're tracking the total time it takes for a request to be responded to. We implemented added custom header: <code>request.headers.add("reqKey",key)</code> 
  with an unique key to the request in Application_AcquireRequestState of our global.asax.cs. </p>
  
  <p>When the Application_PostRequestHandlerExecute is hit for that request, it pulls the custom header with the unique key back out and uses that record the total response time. A bunch of other stuff is also logged with this, such as username, form data, etc., not just simple timings. </p>
  
  <p>This currently works just fine when the code runs on IIS 7.5. However, when it's ran on an ASP.Net Development server, it throws a <code>Operation is not supported on this platform</code> exception. </p>
  
  <p>Our Prod is IIS 7, so should how do I get around this error? </p>