Registration allows "invalid" user names

[AJamesPhillips]

I went to solidcommunity.net and successfully created an account with hyphens in the username. This said it was not allowed but then allowed it anyway?

Your username should be a lower-case word with only letters a-z and numbers 0-9 and without periods.

(Originally posted here: https://github.com/solid/community-server/issues/930 though perhaps this should live on https://github.com/solid/node-solid-server ?)