Source tracking for webinar registrant through API

Is your feature request related to a problem? Please describe.
Like discussed over here Source tracking for webinar registrant through API endpoint url

we are looking for a way to provide the signup source through the API. We have different urls on our side already, which we would like to use also for other use cases. But right now all users that are signin up through this way, have no source attached. It would be great to:

Describe the solution you’d like
Allow passing in a custom source on webinar signup.

Describe alternatives you’ve considered
No alternative solution available