How to extend the generic oidc auth url?

I use auth0 as oidc provider. Auth0 offers the option to append query parameters to the url. In my case I want to specify the connection parameter. Apparently this option is not supported today.
Today, the url is incorrectly composed, making the query parameters invalid.

auth url example: https://dev-igf7ro8x.eu.auth0.com/authorize?connection=google

This results in the following request: https://dev-igf7ro8x.eu.auth0.com/authorize?connection=google?client_id=XXXXX&...

Does anyone have an idea how I can solve this or is such a function planned ?

https://auth0.com/docs/api/authentication#support