In the “Create New ASP.Net Core Web Application” window, select .NET Core as the runtime and ASP.NET Core 2.2 (or later) from the drop-down list at the top. I’ll be using ASP.NET Core 3.0 here.

ASP.NET sees the session cookie and loads the session (or doesn't, and starts a new one). This is why people recommend serving static, unauthenticated resources like images from a separate domain.

Learn the three ways you can return data from your ASP.NET Core Web API action methods.

You can create your own custom modelbinder to solve this problem (I've even discussed how to do that for the ASP.NET Web API). However, that may be overkill. Often you can solve your problem by ...