Central Portal Log Off Issue

Hi All,

we are facing the following issue

1. user logs in to a non sap portal

2. clicks on link which redirects to our SAP Portal

3. user clicks on log off in our SAP Portal and user is redirecting to our SAP Portal log in page

4. when user is clicking Back button in browser it is automatically logging in to the SAP Portal

issue is when user is clicking on browser back button it should not log into our SAP Portal

Please help me in resolving this.

Thanks,

Ram.