There's a newer version of this sample taking advantage of the Microsoft identity platform (formerly Azure AD v2.0)
Check it out: https://github.com/Azure-Samples/ms-identity-aspnetcore-webapp-tutorial, and in particular the first chapters of the tutorial which show how to sign-in a user to a Web app using OpenIDConnect. See 1-WebApp-OIDC
If you really need to access this Azure AD v1.0, you can navigate to the master branch, but please know that it's no longer supported.