how implemente a outside website access the azure ad protected on-premise api

Hi Expert.
I have a on-premise API which I need to expose to outside via azure ad app proxy. and there is one website from internet wants to access this on-premise API. I see there is article describle how to configure native app to access protected API: https://video2.skills-academy.com/en-us/azure/active-directory/manage-apps/application-proxy-secure-api-access

as for the website access the protected API resource, is anything docs I can refer to? my scenarios is like this:

1. when the website wants to access the on-premise API, it will check the user is sign-in or not
2. if user is not sign-in, then ask user to sign-in, after login, website can obtain a access-token
3. website to call the api with the access token

thanks