To customize the domain names to access the Smart WiFi Dashboard and for the splash pages delivered to your hotspots, you must obtain an SSL certificate through GoZone. Please contact your Account Manager to inquire about starting the process.
Check with your specific domain host on how to create CNAME records. As an example, goDaddy Information can be found here: https://www.godaddy.com/help/add-a-cname-record-19236