Check out this 6 1/2 minute video which shows how to redirect users to a login page when the browser session times out. Click the image to see how to build a small application which uses a Login control, Forms Authentication, and the ASPxHttpHandler module:
Using Forms Authentication in an ASP.NET application makes it difficult to redirect users during callbacks. Since Ajax Callbacks only update partial portions of the page. This makes redirecting kind of a pain.
Imagine you have a page that uses a Grid View with callbacks. If a user’s session times out and the user tries to group, sort, page or any operation that does a callback. Then the browser will idle and display the loading icon spinning as the server tries to redirect to the login page.
There is an easy way to handle this. Just add an ASPxHttpHandler module to your web application and it will redirect a callback when the session has timed out.
Check out the video and then leave me note below about how you plan to use this feature.