Firebase Cloud Functions (2nd gen)

Minimum viable example

// functions/src/index.ts
import { onCall, HttpsError } from "firebase-functions/v2/https";

export const hello = onCall((request) => {
  if (!request.auth) throw new HttpsError("unauthenticated", "");
  return { greeting: `hi ${request.auth.uid}` };
});

npx -y firebase-tools@latest deploy --only functions:hello

A signed-in client calls it via httpsCallable("hello"). That's the entire round-trip.