How does wpmudev.org allow usernames with uppercase?

When I signed up for WPMU DEV I created my username with an uppercase character. How can I do this on my own multisite install?

I found this in the forums from 2 years ago and wondering if it's the only solution:

https://premium.wpmudev.org/forums/topic/way-to-allow-uppercase-usernames#post-82055

Thanks!