ASP.NET MVC 4 Membership Overview: http://aaron-hoffman.blogspot.com/2013/02/aspnet-mvc-4-membership-users-passwords.html
I recently developed a website to replace the built in ASP.NET Configuration Website Administration Tool provided by Microsoft and Visual Studio.
Source available here: https://github.com/StoneFinch/SmpMaintenance
Direct link to download source code: https://github.com/StoneFinch/SmpMaintenance/archive/master.zip
This tool has the ability to add new users to a ASP.NET MVC 4 website in bulk. For example, if you have a list of usernames and passwords that you want to set up new accounts for, you can use the "Bulk Add New Users" functionality.
Users can also be added to Roles via this page. Multiple Roles are separated by spaces.
Hope this helps,