Hi @mb_j
We understand your use case. Right the the WebSDK does not support joining a webinar using the join_url from the Add Webinar Register API. However, we will support that in a future release.
The best workaround would be to still generate a unique url for the user with the email and pass in the email to the WebSDK so that they can join the Webinar as that user.
Let us know if that works for you or not.
Thanks