How can I pass referrer data via Universal Login registration

I have developed a game which uses the Auth0 New Universal Login forms, I’ve also configured a url to direct users directly to the signup form using the code below -

returnTo: ‘/’,
authorizationParams: {
screen_hint: ‘signup’

Is it possible to either pass a parameter from the URL through to the registration process, or to have an additional field or similar so that a new user whilst signing up can provide an existing user ID so that we can track who referred them.

An example might be -

Thank you