This page is used to manage the password for the "root" user as well as to create usernames for the purpose of identifying user access for Secure and Private share security modes.
There are some restrictions stemming from linux which apply to usernames:
Usernames must start with a lower case letter or an underscore, followed by lower case letters, digits, underscores, or dashes. They can end with a dollar sign. In regular expression terms:
Usernames may only be up to 32 characters long.