Captive Portal

Is there a way to create a captive portal on my inside interface, then create an exception for the entire network and then allow people to redirect themselves to the portal? As in inside interface is 192.168.0.1/22 so enable the captive portal on the interface. Then create a bypass for the enitre /22 so users aren't redirected by default and just get  matched to the existing policies.

 But if a user needs to get authentication allow them to type in a URL that lands them on the FGT so they can authenticate. This is so they can authenticate against a backend LDAP server if they're using a device that doesn't allow them to sign in with domain creds.