This code is based on an earlier architecture with IdentityServer4 and Ocelot fronting an ASP.NET Core 2.1 API. See the write up on SquareWidget entitled Microservices with IdentityServer4 and Ocelot Fronting a .NET Core API.
For the blog post that accompanies this code see ASP.NET Core 2.1 Web API Using Multiple Authentication Schemes.