Log in as admin Go to Site administration ► Users ► Accounts ► Add a new user Try to create an user using spaces on username field. Make sure you get the validation error message: The username can only contain alphanumeric lowercase characters (letters and numbers), underscore (_), hyphen , period (.) or at symbol (@). Now, try to create the user using capital letters. Make sure you get the validation error message: Only lowercase letters allowed Go to Site administration ► Plugins ► Authentication ► Manage authentication Enable email self registration , don't need to set up anything. Logout. Go to login page and click Create new account button. Try to create an user using spaces on username field. Make sure you get the validation error message: The username can only contain alphanumeric lowercase characters (letters and numbers), underscore (_), hyphen , period (.) or at symbol (@). Now, try to create the user using capital letters. Make sure you get the validation error message: Only lowercase letters allowed