Feature Request: Required Field with Custom Question for Requests to Join a Closed Group

I'm in a Loomio group which is the governance space for another website, and we want to make sure that new people who request to join our Loomio have a presence on that platform as well. As the user-names don't automatically line up, we got to thinking today that it'd be useful to be able to customize and make required the text field that people can current fill in when applying to join a group, so, for instance, we could ask them to share their user name on the other site.