Extension making AJAX requests doesn't get authentication cookies appended

On edge, when a user is logged in to his identity provider (Azure AD), an ajax request to the IDP URL from an extension gets rejected as if the user is not logged in.
Making the same request from a webpage, works as expected.
To my understanding, it has something to do with the PRT mechanism.
If Edge wouldn't wrap the identification by itself, making requests to the IDP from the extension would just work - because it is based on cookies.
But when Edge is managing the process - the cookies are not saved to the domain. Instead, they are appended to each network request created by the web page.
Why isn't the same mechanism apply for requests created by the Extension? Can we get ajax requests to the IDP work?
We need a way to get "inside" the PRT mechanism