I want to make a Xamarin.Forms project, targeting iOS, Android and Windows Phone.

My app needs to authenticate users using Facebook.

Should I implement login for each platform independently, or use a manual flow? https://developers.facebook.com/docs/facebook-login/manually-build-a-login-flow/v2.0

I prefer to have a single implementation of the login flow, and use it on all platforms.

How can I get a single implementaion of the Facebook login flow?