WiFi Guest

Hello,

on Fortigate 800C I already have a captive portal wifi guest access. Of course it is necessary a user ID and a password. However some other guest users would need to automatically authenticate on Fortigate (caching user ID and password or eventually only password) so that they get automatically authenticated so there is no required action by guest. I'm conscious this is not the way captive portal works. Is it possible to achieve it by providing some kind of authentication on Fortigate ?