Firebase Auth Middleware

firebase-auth-middleware.js

'use strict'
require('firebase-functions/lib/logger/compat')

const functions = require('firebase-functions')
const admin = require('firebase-admin')
const express = require('express')
const cookieParser = require('cookie-parser')
const cors = require('cors')

try {
  admin.initializeApp(functions.config().firebase)
} catch (e) {
  // You do that because the admin SDK can only be initialized once.
}

const validateFirebaseIdToken = async (req, res, next) => {
  if (
    (!req.headers.authorization ||
      !req.headers.authorization.startsWith('Bearer '))
  ) {
    res.status(403).send('Unauthorized')
    return
  }

  let idToken
  if (
    req.headers.authorization &&
    req.headers.authorization.startsWith('Bearer ')
  ) {
    idToken = req.headers.authorization.split('Bearer ')[1]
  } else {
    res.status(403).send('Unauthorized')
    return
  }

  try {
    const decodedIdToken = await admin.auth().verifyIdToken(idToken)
    req.user = decodedIdToken
    next()
    return
  } catch (error) {
    res.status(403).send('Unauthorized')
    return
  }
}

const app = express()

app.use(
  cors({
    origin: [
      /.*localhost:\d*/,
      /.*funretro-pro-test\.firebaseapp\.com/,
      /.*easyretro\.io/
    ],
    credentials: true
  })
)

app.use(cookieParser())
app.use(validateFirebaseIdToken)

app.post('/', async (req, res) => {
  res.send({message: 'Hello' })
})

module.exports = functions.https.onRequest(app)