This application shows an example of how Azure AD B2C can be used for authentication in ASP.NET Core 2.1.
It should be noted that I have not yet fully implemented things like error handling.
You will first need to have a B2C directory ready, with an app registered and the various types of policies setup.
After cloning the repository, change values in appsettings.json for ids and callback paths for the different policies (+ client id etc.) from Azure AD B2C.