VPN SSL Web Portal - allow access from domain computers only?

FortiGate 6.0.6 We currently have this config:

config  vpn  ssl web host-check-software     edit "OUR-host-check-windows"         set os-type windows         set type fw         config check-item-list             edit 1                 set type registry                 set target "HKLM\\SYSTEM\\CurrentControlSet\\Services\\Tcpip\\Parameters\\Domain:OUR.DOM"             next         end     next end config vpn ssl web portal     edit "SSL_VPN_Portal_OURS"         set host-check custom         set host-check-policy OUR-host-check-windows     next end A Windows computer that is not registered in our domain, can no longer connect.  But anything not running Windows still can. Is there a way to limit connections to Windows computers registered in our domain only?

Kind regards,

Herta