how to stop multiple login for each user in a session

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[fazz]

hello sir/madam
         i am having one problem after installing endian firewall for authentication . for eg am having 2 users, user 1 and user 2. suppose if user 1 is already logged  in with using his authentications like username and password but  at the same time user 2 should not be  able to logged in with the authentication of user1 username and password so can you please help me to disable the multi login of a single  user in a session.