By default ASP .Net MVC allows developers to customize the way the framework handles user membership. Back in the old days when people used ASP .Net Webforms the main way to do this was to implement a custom membership provider. ASP .Net MVC introduced a new way to do this, using a series of interfaces. In the old way of doing things, a developer had to implement a single abstract class called "MembershipProvider". The new approach pretty much split up this big class into multiple simpler interfaces each providing a part of the functionality of the whole membership system. It is called Identity. It also introduced better support for 3rd party authentication using external systems such as Facebook, Twitter and so on. It is actually built over the old membership system and is available in ASP .Net Core too but it might differ in some ways. The most important interfaces are: IQueryableUserStore and IUserStore, which store the users registered on the website, including th