Here is the scenario.
We have solution built on top of SharePoint 2013 and we are using claims based authentication for external users. We have custom signout page where we delete FedAuth cookie and also send request to identity provider to remove their cookies. When user click on signout, he/she is completely logged out from SharePoint. User has to provide credential again, if they want to sign in. Every thing works great on SharePoint side.
But here is where things got interesting. When user open office document from SharePoint in office client, the office client session remains active. Now if user logout of Sharepoint and does not close the office client, they remains authenticated via office client. If they change document and save, the document got updated and saved in sharepoint. Also if user click on link in the recent documents tab in office client, they are not asked for credentials.
So my question is how can we log out user both from sharepoint and office client when user clicks on sign out in sharepoint?