To redirect to the login page (or any other page) when the session expires, use one of the following methods:
Option 1. Extend the authentication filter chain and implement the desired logic in code. Refer to the following articles for more information: "Configuring authentication filters" and " New security APIs in WebSphere Portal".
Option 2: Modify the ErrorSessionTimeOut jsp to add Java script to redirect to the login page when the session times out. This option is simpler to implement but you may see a momentary "flash" when the redirect occurs.
More information: http://www-01.ibm.com/support/docview.wss?uid=swg21419230