Next.js middleware Module not found: Can't resolve 'fs'

Question

Getting this error in Next.js _middleware file when I try to initialize Firebase admin V9. Anyone know how to solve this issue?

./node_modules/@google-cloud/storage/build/src/bucket.js:22:0
Module not found: Can't resolve 'fs'

../../firebase/auth-admin

import * as admin from "firebase-admin";

if (!admin.apps.length) {
  admin.initializeApp({
    credential: admin.credential.cert({
      projectId: process.env.NEXT_PUBLIC_FIREBASE_PROJECT_ID,
      clientEmail: process.env.FIREBASE_CLIENT_EMAIL,
      privateKey: process.env.FIREBASE_ADMIN_PRIVATE_KEY,
    }),
  });
}

const firestore = admin.firestore();

const auth = admin.auth();

export { firestore, auth };

Calling it in my _middleware

import { NextFetchEvent, NextRequest, NextResponse } from "next/server";
import { auth } from "../../firebase/auth-admin";

export default async function authenticate(
  req: NextRequest,
  ev: NextFetchEvent
) {
  const token = req.headers.get("token");
  console.log("auth = ", auth);
  //   const decodeToken = await auth.verifyIdToken(token);
  return NextResponse.next();
}

I saw a solution here by customizing webpack but this does not fix it.

/** @type {import('next').NextConfig} */
const nextConfig = {
  reactStrictMode: true,
  webpack: (config, { isServer, node }) => {
    node = {
      ...node,
      fs: "empty",
      child_process: "empty",
      net: "empty",
      tls: "empty",
    };
    return config;
  },
};

module.exports = nextConfig;

Answer 1

The Edge Runtime, which is used by Next.js Middleware, does not support Node.js native APIs.

From the Edge Runtime documentation:

The Edge Runtime has some restrictions including:

• Native Node.js APIs are not supported. For example, you can't read or write to the filesystem
• Node Modules can be used, as long as they implement ES Modules and do not use any native Node.js APIs

You can't use Node.js libraries that use fs in Next.js Middleware. Try using a client-side library instead.

Answer 2

I wasted a lot of time tying to get this to work. The weird thing is that this will work in the api itself.

So instead of calling firebase-admin action in the _middleware file. Call it in the api itself like:

import type { NextApiRequest, NextApiResponse } from 'next'
import { auth } from "../../firebase/auth-admin";

export default async function handler(req: NextApiRequest, res: NextApiResponse) {
  const authorization = req.headers.authorization
  console.log(`Handler auth header: ${authorization}`)

  if (!authorization) {
    return res.status(401).json({ message: 'Authorisation header not found.' })
  }

  const token = authorization.split(' ')[1]
  if (!token) {
    return res.status(401).json({ message: 'Bearer token not found.' })
  }

  console.log(`Token: ${token}`)

  try {
    const {uid} = await auth.verifyIdToken("sd" + token)
    console.log(`User uid: ${uid}`)
    res.status(200).json({ userId: uid })
  } catch (error) {
    console.log(`verifyIdToken error: ${error}`)
    res.status(401).json({ message: `Error while verifying token. Error: ${error}` })
  }
}

A workaround to make this reusable is to create a wrapper function.

If anyone knows how to make this work in a _middleware file, I would be really grateful.

Edit: Gist for the wrapper middleware function: https://gist.github.com/jvgrootveld/ed1863f0beddc1cc2bf2d3593dedb6da

Answer 3

make sure you're not calling firebase-admin in the client

import * as admin from "firebase-admin";

Answer 4

I've recently released a library that aims to solve the problem: https://github.com/ensite-in/next-firebase-auth-edge

It allows to create and verify tokens inside Next.js middleware and Next.js 13 server components. Built entirely upon Web Crypto API.

Please note it does rely on Next.js ^13.0.5 experimental "appDir" and "allowMiddlewareResponseBody" features.