Closing user session

I'm attempting to write the code to "logout' of the website.  Currently, when the "Logout" link is clicked I perform the following code:

 
  WebApplication.RedirectURL := WebApplication.ApplicationURL;
 
which works fine... it takes the user back to the login screen, but it starts a new session without releasing the original session.  I have not found the method to release the old session.  I don't want to clear _all_ of the sessions, only the one that belongs to the user that clicked the "logout" button.
 
Thanks,
Scott Gast