Hello,
you could just create a new keycloak user per webinar with:
webinar id = username
webinar secret = password
?
Your real users would then just authenticate with those credentials - though you'd probably need to disable account management for them (and some other self-service operations).
If you add a user indiviual code to the login url that you send to you users then you can associate the login with the actual user (e.g. the email address this link was generated for etc.).
Another option would be to generate a bunch of keycloak users with a limited lifetime, e.g. for the duration of the webinar + x.
When the time is up you could deactivate the users.
In that model you would simply store the email address for each user with the actual keycloak user.
This would enable you to send a concluding "thank you email" and perform some analytics on which individual user did what during the webinar.
Once you're done with you analysis you could delete the users.
Cheers,
Thomas