How can I convert Forms Authentication to windows (Active Directory) authentication

I already have a MVC 5 web application that uses sql server authentication. I am only using AspNetUser and AspNetRole table from EntityFramework and rest are custom tables. Important custom table is UserGroupRole that joins AspNetUser,AspNetRole and a Custom table called UserGroup. 

How can I easily convert this to Windows (Active Directory) authentication and still retain logic that I currently have.  

Or is there an example out there where I can store Active Directory user/group names to a table and then set  website login restriction only to user/group that are in this table

Thanks