medium_post_03

Authenticator.swift

class Authenticator {

    let userDataService = UserDataService()

    func auth(using signInService: SignInService,
              _ completion: @escaping (_ user: User?) -> Void) {

        signInService.signIn { token in
            userDataService.load(forToken: token) { user in
                completion(user)   // note: error handling omitted for brevity
            }
        }
    }
}