custom-token-backend

index.ts

const functions = require('firebase-functions');
const express = require('express');
const cors = require('cors');
const admin = require('firebase-admin');
import {Request, Response} from 'express';

if (admin.apps.length === 0) admin.initializeApp();

const mockAuth = async (id: String, passcode: String): Promise<boolean> => {
  await new Promise(resolve => setTimeout(resolve, 1000));
  return id === 'ABC-1234' && passcode === '123456';
}

const app = express();
app.use(cors({origin: true}));

app.post('/', async (req: Request, res: Response) => {
  const id: String = req.body['id'];
  const passcode: String = req.body['passcode'];
  const authenticated = await mockAuth(id, passcode);
  if (!authenticated) {
    return res.status(400).send({'msg': 'Invalid id or passcode'});
  }
  try {
    const token = await admin.auth().createCustomToken(`MOCK-${id}`);
    return res.status(200).send({
      'id': id,
      'customToken': token
    });
  } catch (e) {
    return res.status(500).send(`Unexpected error while generating custom token.\n${e}`);
  }
});

exports.api = functions.https.onRequest(app);

This is example code I wrote to generate custom token from Firebase Admin SDK.

To know about its uses and practical problems that you will face while coding, read the full article here.