Apple TV (any model) is designed to connect to home networks, where network access may require a name and a password, but doesn’t ask for a username. Set up your Apple TV - Apple Support
For semi-permanent use, the captive portal sign-in credentials for enterprise networks can be included in a device profile, which will make the device automatically sign in every time. When taking the device back home to a different network, you will have to remove the profile again. You –or your network administrator– can add a device profile using Configurator, the tool for enterprise deployments.
Apple Configurator on the Mac App Store - Apple
Apple Configurator - Official Apple Support
Apple Configurator user guide - Apple Support
It may be easier to set up a separate router in between, without captive portal, if this is about a one day use.