how to set require_client_cert on peap with freeradius 2.x

[Jim Shi]

Hi, 
in eap.conf, it says:

 #  You can make PEAP require a client cert by setting

        #

        #   EAP-TLS-Require-Client-Cert = Yes

        #
        #  in the control items for a request.


What does it mean in the control items for a request? On which file? Can someone please help?

Thanks a lot.

Jim