It’s basically simple process.
You may even use the Exchange ready-made firewall publishing policy as base for this one.
This is for SFOS 17.X

So, let’ move on:

1.      I assume you already have the SSL certificate installed properly on the XG box.

2.      Need to add the ADFS server to have a name under "Hosts andServices"

3.      Create new "Web Server" entry and use the host you added in step 1

4.      Create new protection policy with these settings:

a.       Set “Mode” to “Monitor”. You may use “Reject” if you’re concerned.

b.      Enable “Block clients with bad reputation”.

c.       Enable “Common threat filter”.

5.      Create new business rule with these settings:

a.       Hosted address “#Port2” assuming it’s the WAN port.

b.      Enable “HTTPS”.

c.       Select the SSL certificate, and add the URL under “Domains”.
For example “adfs.as7ablog.com”.

d.      Under “protected server(s)” select the ADFS server.

e.       Select the “Any IPv4” under “Access permission”.

f.        Select the protection policy you’ve created on step 4.

g.      Select the intrusion prevention policy if you like to.

h.      Enable "Pass host header"