ASP.NET Core Identity is an API from Microsoft to manage users in ASP.NET Core applications and includes support for integrating authentication and authorization into the request pipeline.
ASP.NET Core Identity is a toolkit with which you create the authorization and authentication features an application requires. There are endless integration options for features such as two-factor authentication, federation, single sign-on, and account self-service. There are options that are useful only in large corporate environments or when using cloud-hosted user management.