Live Code runs in IIS and ASP.NET Web Server but not IIS Express

Having recently installed IIS Express I was hoping that it was going to make life easier for me, but I've run into a problem almost straight away.

Consider the following which is representative of some live code:

Public Shared Function GetServiceId() As String

  Dim principal As MyCustomAuthentication.Principal.MyPrincipal

  principal = CType(Thread.CurrentPrincipal, MyCustomAuthentication.Principal.MyPrincipal)
  .
  .
  .
  .

End Function

Running the code under the ASP.NET Web Server (Cassini) everything is fine and I can see that Thread.CurrentPrincipal is of type MyCustomAuthentication.Principal.MyP开发者_如何学JAVArincipal.

Running under IIS Express this same line throws an InvalidCastException and checking the type I find it is now of System.Security.Principal.GenericPrincipal which is confusing as nothing else has changed.

I can confirm that MyCustomAuthentication.Principal.MyPrincipal implements IPrincipal and remember this is Live code, it is currently deployed and working.

Can anyone shed any light on what is going on here?

I think you want HttpContext.Current.User instead. The identity of the current User isn't the same as the identity of the current thread.