OpenIddict
Versatile OpenID Connect stack for ASP.NET Core and Microsoft.Owin
...Developers looking for a simple and turnkey solution are strongly encouraged to use OrchardCore and its OpenID module, which is based on OpenIddict, comes with sensible defaults and offers a built-in management GUI to easily register OpenID client applications. Unlike many other identity providers, OpenIddict is not a turnkey solution but a framework that requires writing custom code to be operational (typically, at least an authorization controller), making it a poor candidate for the certification program. While a reference implementation could be submitted as-is, this wouldn't guarantee that implementations deployed by OpenIddict users would be standard-compliant.