Can I use captive portal and user control only with base license

Hello TVV,
Thank you for reaching out to the community, Base License offers: Stateful Firewall, VPN, Wireless. So you should be able to access those services. 
> Licensing - https://docs.sophos.com/nsg/sophos-firewall/18.5/Help/en-us/webhelp/onlinehelp/AdministratorHelp/Administration/Licensing/index.html

Hi TVV

Thank you for reaching out to the community, you can authenticate users with Captive Portal but if you want to protect your network license is required.

Thanks and Regards