Hi Zeph
We’ve built an integration in to Alta for the external captive portal, we’ve enabled auto email verification on our platform , we’ve not enable the OTP we’ve found issues when the customer has no cell signal. But it’s on our list to build check out www.captivewifi.io or drop me message at adam@captivewifi.io as we’ve giving away 2 months free usage - no catch. We can switch you on in 30 seconds.
Adam
@captivewifi is probably the best current answer. It is a paid option like they said but offers that customization. The Alta hotspot portal is just password. Your router may have an option as well with a few more features i know OPNsense has a captive portal for guest networks. It uses voucher codes so i believe you can setup a server to hand those out. Guest would fill out their email or a forum and as code would be created and emailed.