Site members signing up for webinars via API

I have an online community, with members whose name and email addresses I know, but I am a bit confused about how to make a very simple single button registration for webinars I have scheduled. I do NOT want them to fill out any form at all (winth info I already know!), I just want a click and they are in (and a click to unregister).

I have gotten the OAuth process to work in sample code that gets called back when I execute the authorization URL,getting the code and using that to get auth tokens, but how does that translate into just allowing members to see one button at my website that says “Register”, and probably another button that says “Unregister” if I see they are signed up for that webinar?

I did create a table in my DB for storing access and refresh tokens, am I meant to just use those to allow my site membes to add themselves or remove themselves from scheduled webinars (via server side code of course)? And, if so, how long do refresh tokens last? Forever? I mean, if I create the access token manually (using the authorize call for my SDK app), then store both the access and refresh tokens in the DB table, can I use those forever and never need to do an authorization again?

Most of this is about process flow, how I allow a random site member, at any given random point in time, to add themselves my webinars. I am assuming I do not need to call the authorize endpoint all the time once I have gotten the tokens, and certainly if a member wants to get on the list for a webinar, having to have someone click on an Allow Access button makes no sense whatsoever.

Any illumination on how to acheive this simple UX flow would be great, geting a sample endpoint working to get tokens and store them is fine but implementing the whole system in my custom-coded PHP website is a bit confusing.

Ben Cahan