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This guide will show you can use thirdweb Auth as a custom authentication provider for Firebase, and automatically create a document in the users Firestore collection when a user signs up successfully.

We'll be using Next.js to build the example project.


Set Up

To begin with, let's create a new Next.js project with the SDK configured:

npx thirdweb create --app --next --ts

From within the created directory, we need to install @thirdweb-dev/auth, firebase and firebase-admin:

npm install @thirdweb-dev/auth firebase firebase-admin

Configure Firebase

We'll use environment variables to store our Firebase configuration.

Create a .env.local file in the root of your project and add the corresponding values from your Firebase project:


Create a new directory called lib and create two helper scripts to initialize Firebase in the browser and server:

Now we have an easy way to access Firebase Auth and Firestore in both client and server environments!

Wallet Private Key

We use our wallet's private key to instantiate the SDK on the server-side.

We recommend using a Secret Manager to secure your private key.

Environment Variables for private keys

In this guide, we'll use environment variables for simplicity; but this is a security vulnerability and not recommended best practice for production environments.

Inside our .env.local file, add an environment variable to store your wallet's private key:



Inside the pages/_app.tsx file, configure the authConfig option:

import type { AppProps } from "next/app";
import { ChainId, ThirdwebProvider } from "@thirdweb-dev/react";

// This is the chainId your dApp will work on.
const activeChainId = ChainId.Mumbai;

function MyApp({ Component, pageProps }: AppProps) {
return (
// The backend URL of the authentication endoints.
authUrl: "/api/auth",
// Set this to your domain to prevent signature malleability attacks.
domain: "",
// The redirect URL after a successful login.
loginRedirect: "/",
<Component {...pageProps} />

export default MyApp;

Sign Up / Log In Users

The process of creating users in Firebase by authenticating them with their wallet has two steps:

  1. Authenticate the user with their wallet
  2. Create a user in Firebase with the knowledge that they own this wallet

On the homepage (pages/index.tsx), we'll allow the user to connect their wallet and then sign in with Ethereum.

import React from "react";
import { ConnectWallet, useAddress, useSDK } from "@thirdweb-dev/react";
import { doc, serverTimestamp, setDoc } from "firebase/firestore";
import { signInWithCustomToken } from "firebase/auth";
import initializeFirebaseClient from "../lib/initFirebase";

export default function Login() {
const address = useAddress();
const sdk = useSDK();
const { auth, db } = initializeFirebaseClient();

return (
{address ? (
<button onClick={() => signIn()}>Sign in with Ethereum</button>
) : (
<ConnectWallet />

The signIn function:

  1. Makes a request to the api/auth/login endpoint to get a custom token from Firebase
  2. Signs the user in with the custom token
  3. Creates a user in Firestore with the verified user's address
// Note: This function lives inside the Login component above.
async function signIn() {
// Use the same address as the one specified in _app.tsx.
const payload = await sdk?.auth.login("");

// Make a request to the API with the payload.
const res = await fetch("/api/auth/login", {
method: "POST",
headers: {
"Content-Type": "application/json",
body: JSON.stringify({ payload }),

// Get the returned JWT token to use it to sign in with
const { token } = await res.json();

// Sign in with the token (creates a Firebase user)
signInWithCustomToken(auth, token)
.then((userCredential) => {
// On success, we have access to the user object.
const user = userCredential.user;

// If this is a new user, we create a new document in the database.
const usersRef = doc(db, "users", user.uid!);
if (!usersRef) {
// User now has permission to update their own document outlined in the Firestore rules.
setDoc(usersRef, { createdAt: serverTimestamp() }, { merge: true });
.catch((error) => {

In this function, you'll notice we're calling the /api/auth/login endpoint to get a custom JWT token from Firebase.

Let's take a look at that API route.

Auth API Route

Create a folder that lives in the /pages/api/auth directory called login.ts.

This API route is responsible for:

  1. Verifying the payload provided by the client
  2. Once the payload is verified, creating a custom token for the user to sign in to Firebase with.
import { NextApiRequest, NextApiResponse } from "next";
import { ThirdwebSDK } from "@thirdweb-dev/sdk";
import initializeFirebaseServer from "../../../lib/initFirebaseAdmin";

export default async function login(req: NextApiRequest, res: NextApiResponse) {
// Grab the login payload the user sent us with their request.
const loginPayload = req.body.payload;
// Set this to your domain to prevent signature malleability attacks.
const domain = "";

const sdk = ThirdwebSDK.fromPrivateKey(
// Using environment variables to secure your private key is a security vulnerability.
// Learn how to store your private key securely:
"mumbai", // configure this to your network

let address;
try {
// Verify the address of the logged in client-side wallet by validating the provided client-side login request.
address = sdk.auth.verify(domain, loginPayload);
} catch (err) {
// If the login request is invalid, return an error.
return res.status(401).send("Unauthorized");

// Initialize the Firebase Admin SDK.
const { auth } = initializeFirebaseServer();

// Generate a JWT token for the user to be used on the client-side.
const token = await auth.createCustomToken(address);

// Send the token to the client to sign in with.
return res.status(200).json({ token });

You'll now be able to use Firebase Authentication to authenticate users with their wallets!

Firestore Rules (Optional)

You'll likely want to add a security rule to your Firestore database that only allows users to update their documents.

rules_version = '2';
service cloud.firestore {
match /databases/{database}/documents {
// The wildcard expression {userId} makes the userId variable available in rules.
match /users/{userId} {
// Only allow users to update their own documents.
allow create, update, delete: if request.auth != null && request.auth.uid == userId;
// But anybody can read their profile.
allow read;

Viewing the Result

When you click the "Sign in with Ethereum" button and successfully sign in, you'll be signed up as a user in Firebase:

Firebase Users

And a new document will be created in your users collection in Firestore:

Firestore Users

You can now use all the functionality of Firebase Authentication and Firestore to build your app!

What's Next?

In our example repository, we have additional functionality available to: