Destroying or Deleting the Authid cookie in forms session before calling rwservlet

I have a need for a user within a forms session to issue report requests to rwservlet using multiple user credentials.  I am able to set the value of the user credentials within the Authid cookie before the first report is run.  However, I am unable to change the user credentials within the cookie once they were set the first time.

I need to be able to delete/destroy the Authid cookie from within the form session whenever a new report request is issued so that I can dynamically set the user credentials for the next report request.  This would also allow me to expire the cookie quickly.  Now, once the cookie has expired, I am unable to reset the expiration time within the cookie and the user is constantly prompted for their credentials.