ASP.net Web API, redirect to OAuth2 service

I am a beginner to OAuth2. Within our company we have written an authentication microservice which authenticates any Windows users and returns a Bearer token.

In the ASP.net Web API project that I am working on, I need to implement OAuth2 and I should use the authentication microservice mentioned above.

How do I setup the Oauth sepcifically OAuthAuthorizationServerOptions? How do I redirect the users if they are not authenticated to the microservice? Do I need an AccountController to redirect the users to the microservice?

A sample code will be helpful.