Allow requiring suffix/prefix on usernames to avoid conflicts with LDAP usernames
We are a site which has both internal staff (authenticated via LDAP) and want to allow external contributors to sign up via the web interface. The problem is that we can't allow a username to be created / chosen which may later conflict with an LDAP one. It would be useful to be able to require signups to have something like USERNAME-ext or ext-
USERNAME as their username so that we can avoid this problem. For now, we've had to disable external signups which isn't ideal as it limits interaction with external people.