Has anyone built a feature to retrieve a user's username? There is a Forgot my Password but you have to provide your username and since you can't duplicate this between orgs I'd like to build this self service functionality. 

I was thinking of a lightning page where you enter your email, then the page checks for active users with that email and if none, shows an error. If found, it could trigger a templated email to their email with their username. Anyone done something similar?