UserSearchViewController.swift

func authUI(_ authUI: FUIAuth, didSignInWith authDataResult: AuthDataResult?, error: Error?) {
    if let error = error {
        print(error.localizedDescription)
    } else {

        //Save the user to our list of users.
        if let user = authDataResult?.user {
            let ref = Database.database().reference()
            ref.child("users").child(user.uid).setValue(["username" : user.displayName?.lowercased(),
                                                         "displayname" : user.displayName,
                                                         "email": user.email])
        }
    }
}