Possible to add new user which is not inside your Window Domain?

Discussion created by MayMay on Nov 1, 2013
Here is our current ArcGIS server security configuration settings:
User store:  Windows Domain
Role Store: ArcGIS Server Built-in
Authentication Tier: GIS Server
Authentication Mode:  ArcGIS Tokens
I would like to know that is there possible to create a user who is not in the window domain but able to access to view all the secured services by entering username & password on web application.
I follow this step here ( but "New User" button is being gray out.  Hope someone can give me some ideas how to do so.
Thank you.