Is it possible to change FortiProxy captive portal cert to my company wildcard cert?

Hey chin23,

you should be able to set a certificate under Users&Devices > Authentication settings, I believe, for captive portal purposes. If the issue is with replacement messages, you need to set the server certificate under System Settings instead, and if the issue is with Deep Inspection, you need to create a CA certificate and import that to FortiProxy to use in an SSL inspection profile.