Route All Users Connected Through a Specific Intermediate to a Site

Hello,

We use Fortigate 1500D Firewall.

I have created an VLAN such as EduroamVLAN. It's IP/Network Mask is 10.74.0.1/255.255.0.0. And I have created an wireless interface such as EduroamHelpNet. EduroamHelpNet is fully open. So it's don't have any security protection.

When a user connects to EduroamHelpNet  and wants to go to any site or address, I want to forward this user to such help.domain.edu. So people connected to this network will only be able to access this site.

In this site we have Eduroam configuration docs for operating systems.

How can I do this?

Best regards.