It seems that the FormsAuthenticationModule gets handled first. This module is normally earlier than any custom module in the ASP.NET pipeline, so when AuthenticateRequest is fired, FormsAuthenticationModule will get called first, do its job and then your module’s event handler will be called. If you really want to dig deep into this, I suggest trying … Read more
Maybe this helps http://support.microsoft.com/kb/307985/en-us/ An HttpApplication class provides a number of events with which modules can synchronize. The following events are available for modules to synchronize with on each request. These events are listed in sequential order: BeginRequest AuthenticateRequest AuthorizeRequest ResolveRequestCache AcquireRequestState PreRequestHandlerExecute PostRequestHandlerExecute ReleaseRequestState UpdateRequestCache EndRequest The following events are available for modules to … Read more