How to Persist a Logged-in User in React: A Comprehensive Guide

Persisting a user‘s logged-in state is a critical part of building a great authentication experience. It allows users to stay authenticated as they navigate through your app, without the frustration of repeatedly entering their credentials.

In fact, a study by the Baymard Institute found that 37% of users will abandon their online shopping cart if they are forced to create an account (Holst, 2021). By persisting login state and supporting guest checkout, you can reduce friction and boost conversion rates.

In this comprehensive guide, we‘ll cover everything you need to know about persisting logged-in users in a React application, including:

• An overview of different persistence techniques and their tradeoffs
• A complete code example of using localStorage to keep users logged in
• Security best practices for handling sensitive auth data
• Guidance on when to use localStorage vs. other persistence methods

By the end, you‘ll have a solid understanding of how to build secure and user-friendly authentication in React. Let‘s get started!

Authentication persistence techniques compared

There are several ways to persist a user‘s logged-in state in a web application. Let‘s compare the most common techniques:

Technique	Pros	Cons
localStorage	Simple to use, data persists across sessions	Limited to 5MB per domain, vulnerable to XSS attacks
Cookies	Automatically sent with server requests, can be marked as HTTP-only and Secure	Limited to 4KB per cookie, requires server-side handling
Session storage	Similar to localStorage but scoped to the browser session	Data is lost when session ends (e.g. closing the browser)
Server-side sessions	Allows for more centralized control and security	Requires server-side setup and handling, may not scale well
JSON Web Tokens (JWT)	Stateless authentication, can store user data directly in token	Token size can bloat with more user data, tokens can‘t be revoked

As a general rule, localStorage is a good choice for simpler applications that only require persisting a lightweight user object or authentication token. It‘s easy to use and doesn‘t require any server-side handling.

However, localStorage has some security vulnerabilities, such as being accessible to any JavaScript code running on the same domain. It‘s important to follow security best practices, which we‘ll cover more later on.

For more complex applications that need to store additional user data or have stricter security requirements, server-side sessions or JWTs may be a better fit. These approaches allow for more fine-grained control over session expiration and can provide additional security measures like CSRF protection.

Persisting logged-in users with localStorage

Now let‘s walk through a complete example of using localStorage to persist a logged-in user in a React application.

Here‘s the basic flow:

1. When a user successfully logs in, store a user object or authentication token in localStorage
2. On subsequent page loads, check localStorage for the presence of a user object or token
3. If found, use the stored data to set the initial authenticated state of the application
4. Include logic to handle expiration and refresh of stored tokens
5. Clear localStorage when the user logs out

Here‘s a simplified version of the code:

import React, { useState, useEffect } from ‘react‘;
import axios from ‘axios‘;

const App = () => {
  const [user, setUser] = useState(null);

  useEffect(() => {
    // Check localStorage for a stored user on mount
    const storedUser = localStorage.getItem(‘user‘);
    if (storedUser) {
      setUser(JSON.parse(storedUser));
    }
  }, []);

  const handleLogin = async (username, password) => {
    try {
      // Send login request to server
      const res = await axios.post(‘/api/login‘, { username, password });

      // Store user object in localStorage
      localStorage.setItem(‘user‘, JSON.stringify(res.data.user));

      // Update user state
      setUser(res.data.user);
    } catch (err) {
      console.error(err);
    }
  };

  const handleLogout = () => {
    // Remove stored user and reset user state
    localStorage.removeItem(‘user‘);
    setUser(null);
  };

  if (user) {
    return <AuthenticatedApp user={user} onLogout={handleLogout} />;
  } else {
    return <LoginForm onLogin={handleLogin} />;
  }
};

Let‘s break this down further:

• In the useEffect hook, we check for a stored user object in localStorage when the component mounts. If found, we parse the JSON string and update state.
• The handleLogin function sends a login request to the server with the provided credentials. If successful, we store the returned user object in localStorage as a JSON string, and update the user state.
• The handleLogout function removes the stored user from localStorage and resets the user state to null.
• Finally, we conditionally render either an AuthenticatedApp component if there‘s a logged-in user, or a LoginForm component if not.

This is a simplified example, but it demonstrates the core concepts of using localStorage to persist login state. In a real-world application, you‘d want to add additional features like:

• Handling token expiration and refresh
• Checking for a valid stored user on every authenticated request
• Showing a loading state while checking for a stored user on mount
• Handling errors and edge cases

Security considerations

When storing authentication data in localStorage, it‘s critical to follow security best practices to protect your users‘ data. Here are some key considerations:

1. Only store sensitive data in localStorage if your app is served over HTTPS. This encrypts data in transit and helps prevent man-in-the-middle attacks.

2. Don‘t store plain-text passwords or other sensitive data in localStorage. Instead, store a hashed or encrypted version of the data, and only decrypt it on the server-side.

3. Set reasonable expiration times on any stored tokens, and include logic to refresh them periodically. This helps limit the damage if a token is compromised.

4. Use the HttpOnly and Secure flags on authentication cookies to prevent client-side access and require HTTPS transmission.

5. Implement server-side security measures like CSRF protection and rate limiting on authentication endpoints.

6. Clear any stored authentication data from localStorage when a user logs out, and provide a way for users to manually log out of all sessions.

7. Regularly audit your application for security vulnerabilities and keep all dependencies up to date.

By following these best practices, you can help protect your users‘ data and prevent unauthorized access to your application.

Conclusion

Persisting a user‘s logged-in state is a crucial part of building a seamless authentication experience in React applications. By using localStorage, we can store a user object or authentication token that keeps the user authenticated across page loads and browser sessions.

The key steps are:

1. Storing the user object or token in localStorage upon successful login
2. Checking for the presence of stored data on subsequent page loads and setting the initial authenticated state
3. Handling token expiration and refresh
4. Clearing localStorage when the user logs out

While localStorage is a simple and convenient option, it‘s important to carefully consider the security implications and follow best practices for protecting sensitive data.

For more complex applications, server-side sessions or JSON Web Tokens may provide additional security and flexibility.

As a full-stack developer, it‘s important to understand the tradeoffs between different persistence techniques and choose the approach that best fits the needs of your application and users.

By following the guidance in this article and staying up-to-date with industry best practices, you‘ll be well-equipped to build secure and user-friendly authentication in your React applications.

References

• Holst, C. (2021). 37% of Users will Abandon Their Online Shopping Cart if Forced to Create an Account (New Data). Baymard Institute. Retrieved from https://baymard.com/blog/guest-checkout-account-abandonment