Identityserver4 setup for native mobile app with custom and social login

Trying to get my head around the Identityerver4 setup for my project. I have a mobile app where users should be able to login with either facebook or username/password. Facebook login is implemented using the native facebook if available on the device. This results in a token from facebook. With this token I want to request an access_token and refreshtoken (hybrid flow) to access my api (resource). At the same time, some users will also log in unsing username and password. As I need some info about the user, my plan is to user ASPNET Identity but I'm not sure how to make it wotk together with IdentityServer and If user profiles should be created in Identity based on both logins (registration). It seems obvious for the username/password login, but what about my social facebook login. Later there might also be a web client. So my basic question is how to handle the user registration with both setups