try    The  client  certificate is requested.  If no certificate
                     is provided, the session proceeds  normally.   If  a  bad
                     certificate  is  provided,  the  session  is  immediately
                     terminated.

              demand | hard | true
                     These keywords  are  all  equivalent,  for  compatibility
                     reasons.   The  client  certificate  is requested.  If no
                     certificate  is  provided,  or  a  bad   certificate   is
                     provided, the session is immediately terminated.