This repo contains a sample of migrating the ASP.NET Core Web Application Template in Visual Studio 2015 (with Individual User Accounts) from to use MongoDB for the Identity framework. Basically storing users and roles in MongoDB instead of MSSQL/EntityFramework.
Review the commit log for the steps taken, I made individual small commits with comments at each step.
This repo also contained the older sample steps for the v2 Identity framework with ASP.NET, watch out for that as the steps aren't the same with v3 Identity and ASP.NET Core.