React + Express Authentication Guide | PropelAuth

Announcing MCP Authentication: secure your MCP servers with PropelAuth

In this guide, we’ll build an example application in React/Express where users can sign up, login, and manage their accounts. We'll include social logins (Login with Google), passwordless logins, and allow our users to upload their own profile pictures.

We're going to use the following technologies for this blog post:

React.js - for our frontend
Express (Node.js) - for our backend
PropelAuth - for user login and management

The code is available on GitHub in these two repos: React and Express.

Setting up Authentication

PropelAuth fully manages your signup, login, and account management flows. Features like social login (Login with Google), passwordless/magic links, and 2FA for our end users can be enabled in one click. You can sign up here.

The first thing to do after you sign up is create your project:

Afterwards, a test environment is created for you.

Your default login page includes login, signup, account pages, and optional organization management pages. There's a default logo, color scheme, and both passwordless and password-based login. You can fully test what your end users will experience, transactional emails included, but you might want to configure its style first in your dashboard under the Hosted Auth Pages section.

From here, you can configure other aspects of your end-users auth experience, including:

Adding "Login in with Google" or other SSO providers
Collecting additional metadata on signup - like username or first name/last name
Allowing your users to upload their own profile picture
Letting your end-users create organizations and invite their coworkers (called B2B support)

After configuring your project, it's now time to integrate it with your frontend and backend.

Authentication in React

One of the benefits of having PropelAuth manage your users is you can use whatever frontend or backend you want - or even migrate between them. In this case, we'll use React.js.

Creating a new React project

If you don't have a project already, you'll want to follow the official instructions and run:

$ npx create-react-app frontend

Installation

The @propelauth/react package provides an easy interface to access your users' information and manage auth tokens.

$ yarn add @propelauth/react

Setup

At the top of our application, we will add our AuthProvider

import {AuthProvider} from "@propelauth/react";

ReactDOM.render(
    <AuthProvider authUrl={process.env.REACT_APP_PROPELAUTH_AUTH_URL}>
        <App/>
    </AuthProvider>,
    document.getElementById('root')
);

The authUrl is available on the Frontend Integration section of your PropelAuth project.

When a user logs in to our hosted pages, a secure, HTTP-only cookie is set. The AuthProvider checks if the user is logged in, fetches auth tokens and user information. In production, you must use a custom domain to avoid third-party cookie issues.

Usage

withAuthInfo injects user information into your React components. Example:

import {withAuthInfo} from '@propelauth/react';

function AuthInfoOnFrontend({user}) {
    return <span>
        <h2>User Info</h2>
        {user && user.pictureUrl && <img src={user.pictureUrl} className="pictureUrl" />}
        <pre>user: {JSON.stringify(user, null, 2)}</pre>
    </span>
}

export default withAuthInfo(AuthInfoOnFrontend);

If we add this component to our App and visit our site before logging in, we'll see:

After logging in, we'll see:

In addition to user, withAuthInfo also injects isLoggedIn, accessToken, and orgHelper.

Creating Login/Logout Buttons

@propelauth/react provides React hooks for user redirection to login/signup/account pages. Example:

import {withAuthInfo, useLogoutFunction, useRedirectFunctions} from '@propelauth/react';

function AuthenticationButtons({isLoggedIn}) {
    const logoutFn = useLogoutFunction();
    const {redirectToSignupPage, redirectToLoginPage, redirectToAccountPage} = useRedirectFunctions();

if (isLoggedIn) {
        return <div>
            <button onClick={redirectToAccountPage}>Account</button>
            <button onClick={() => logoutFn()}>Logout</button>
        </div>;
    } else {
        return <div>
            <button onClick={redirectToSignupPage}>Signup</button>
            <button onClick={redirectToLoginPage}>Login</button>
        </div>;
    }
}

export default withAuthInfo(AuthenticationButtons);

Making authenticated requests

To make an authenticated request on behalf of your user, provide the access token in the Authorization header:

Authorization: Bearer ACCESS_TOKEN

Example using fetch:

function fetchWhoAmI(accessToken) {
    return fetch("/whoami", {
        headers: {
            "Content-Type": "application/json",
            "Authorization": `Bearer ${accessToken}`
        }
    }).then(response => {
        if (response.ok) {
            return response.json();
        } else {
            return {status: response.status};
        }
    });
}

You can use React's useEffect hook for this:

import {withAuthInfo} from "@propelauth/react";
import {useEffect, useState} from "react";

function AuthenticatedRequestToBackend({accessToken}) {
    const [response, setResponse] = useState(null);

useEffect(() => {
        fetchWhoAmI(accessToken).then(setResponse);
    }, [accessToken]);

return <span>
        <h2>Server Response</h2>
        <pre>{response ? JSON.stringify(response, null, 2) : "Loading..."}</pre>
    </span>;
}

export default withAuthInfo(AuthenticatedRequestToBackend);

A quick note on CORS

To fix CORS issues, add the following to your package.json:

"proxy": "http://localhost:3001"

Authentication in Express

Creating an unprotected route

First, we install express and dotenv:

$ mkdir backend
$ cd backend
$ npm init
$ npm install --save express dotenv

Then, create the route our frontend expects (/whoami):

require('dotenv').config();
const express = require('express');
const app = express();
const port = 3001;

app.get('/whoami', (req, res) => {
    res.json({'test': 'test'});
});

app.listen(port, () => {
    console.log(`Example app listening at http://localhost:${port}`);
});

Protecting our route

Our frontend passes an access token, and now we’ll use PropelAuth’s Express library @propelauth/express to validate the user:

$ npm install --save @propelauth/express

Protecting the API:

// New file: propelauth.js
const propelAuth = require('@propelauth/express');

module.exports = propelAuth.initAuth({
    authUrl: process.env.PROPELAUTH_AUTH_URL,
    apiKey: process.env.PROPELAUTH_API_KEY,
});

// back in index.js
const {requireUser} = require('./propelauth');
app.get('/whoami', requireUser, (req, res) => {
    res.json({userId: req.user.userId});
});

Wrapping up

In under 100 lines of code, we built an advanced application with PropelAuth taking care of authentication. We’ve made authenticated requests from frontend to backend, identifying users based on their requests.