use-firebase-user

A higher order function that decodes a Firebase Auth JWT and decorates the NextJS API request object with a Firebase user.

Introduction

I wanted to use Firebase Auth to authenticate and secure routes in my NextJS API.

The Problem

• Unable to add middleware to express middleware chain for NextJS API routes.
• Don't want to add a large library for a lightweight operation to be run on a serverless function.

My Solution

• Follow the Verify ID Tokens using a third party JWT library instructions from the firebase auth docs to securely verify and decode the JWT.
• Write a higher order function to decorate the NextJS request object with authenticated Firebase user data.

Installation

npm i --save with-firebase-user

or

yarn add with-firebase-user

Usage

Pass your NextJS handler to withFirebaseUser and it will add the authenticated user to the request object user key.

import { withFirebaseUser } from 'with-firebase-user';

const handler = async (req, res) => {
  res.send(req.user); // FirebaseUser
};

export default withFirebaseUser(handler);

Make sure to add your JWT to the request headers on the client.

fetch('/api/users', {
  headers: {
    Authorization: 'Bearer <JWT>',
  },
});

Decoded user data

interface FirebaseUser {
  name?: string;
  user_id: string;
  email?: string;
  email_verified?: boolean;
}

API

const withFirebaseUser: (
  handler: (
    req: NextApiRequestWithFirebaseUser,
    res: NextApiResponse
  ) => Promise<void>,
  options?: WithFirebaseUserOptions | undefined
) => (req: NextApiRequest, res: NextApiResponse) => Promise<void>;

WithFirebaseUserOptions (passed as a second argument to withFirebaseUser function)

interface WithFirebaseUserOptions {
  clientCertUrl?: string; // defaults to url provided in Firebase auth docs
  projectId?: string; // verifies the audience and issuer of the JWT when provided
}