firebase microservices function example from https://medium.com/@jthegedus/scaling-firebase-973f71074f72

auth-src-index.ts

import { onNewUser } from "./onNewUser/function";

// functions in this object will be prefixed with "users"
// Eg: auth-onNewUser
const auth = { onNewUser };

export { auth };

auth-src-onNewUser-function.ts

import * as functions from "firebase-functions";
import * as admin from "firebase-admin";

const addNewUser = functions.auth.user().onCreate(user => {
  // …
});