I found the following pages and they walk through the steps to accomplish this. They work.

• Facebook, Google, and external provider authentication in ASP.NET Core
• Microsoft Account external login setup with ASP.NET Core
• Google external login setup in ASP.NET Core

I didn't copy those web pages across to here because that's a 1/2 hour job or longer. With a -1 vote I'm figuring this is not a topic of interest for others, so not worth the time.