Help with two .NET SSO Okta apps

I have two .NET apps, one .NET 4.X web forms and the other a .NET Web API app. I have configured each app to use Okta for authentication so that if I go to one and login and then go to the other directly it will recognize that I am logged in and not ask for my credentials again.

What I need is for the Web Forms app to call the Web API to get some resources, however when I do this (using a WebRequest on the server side) I get the login page as a response. I did some searching but since I am new to Okta I am limited by not knowing what this specific flow is called.

  1. If I am logged in to the Web Forms app how do I pre-authenticate the request I make to the Web API?
  2. What is this Okta flow called?
  3. In this flow would I need to pass an id_token or access_token to the Web API?

Appreciate any help.