Hello Rien,
I believe you would have to begin with the user guide: https://emc.extremenetworks.com/content/oneview/docs/control/access_control/docs/portal_config/l_ov_ia_captive_portal_config.htm
You could go to Access Control configuration, and for Captive Portal features you'd have to select Guest Web Access or Guest Registration feature, then you'll be free to customize the feature so it would only require AUP acknowledgement. But how about putting some more security over there?
If you need more assistance with that, let us know. I've no problem with doing some remote session on this.
Hope that helps,
Tomasz