Supabase Client-Side Auth in Next.js: A Complete Guide

Hey guys! So, you’re diving into building awesome apps with Next.js and want to get Supabase client-side auth working smoothly? You’ve come to the right place! In this ultimate guide, we’re going to break down exactly how to implement secure and seamless client-side authentication using Supabase with your Next.js application. We’ll cover everything from setting up your Supabase project to handling sign-up, login, log out, and protecting your routes. Whether you’re a seasoned developer or just starting out, this article will equip you with the knowledge and code snippets you need to get your auth flow up and running in no time. Let’s get this party started!

Getting Started with Supabase and Next.js

First things first, Supabase client-side auth in Next.js is all about making your user management a breeze. Before we can even think about authentication, you need a Supabase project. If you don’t have one yet, head over to Supabase.com and sign up for free. Once you’re in, create a new project. You’ll get a Project URL and a anon public key, which are super important for connecting your Next.js app to your Supabase backend. Keep these handy!

Now, let’s get your Next.js project set up. If you haven’t already, you can create a new Next.js app using create-next-app :

npx create-next-app@latest my-supabase-auth-app
cd my-supabase-auth-app

Next, you’ll need to install the Supabase JavaScript client library:

npm install @supabase/supabase-js

Or if you’re using yarn:

yarn add @supabase/supabase-js

With the library installed, it’s time to initialize Supabase in your Next.js app. Create a new file, maybe utils/supabaseClient.js , and paste the following code:

import { createClient } from '@supabase/supabase-js';

const supabaseUrl = process.env.NEXT_PUBLIC_SUPABASE_URL;
const supabaseAnonKey = process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY;

export const supabase = createClient(supabaseUrl, supabaseAnonKey);

Make sure to add your Supabase URL and anon key to your .env.local file as environment variables:

NEXT_PUBLIC_SUPABASE_URL=your_supabase_project_url
NEXT_PUBLIC_SUPABASE_ANON_KEY=your_supabase_anon_key

Remember to replace the placeholders with your actual Supabase project URL and anon key . These NEXT_PUBLIC_ variables are crucial because they allow you to access them directly in the browser, which is exactly what we need for client-side authentication. This setup is the foundation for all your Supabase client-side auth Next.js interactions. It’s pretty straightforward, right? This initial step is vital, as it establishes the connection between your frontend and your Supabase backend, paving the way for all the authentication magic we’re about to perform. We’re building the bridge, guys!

Implementing User Sign-Up

Alright, now that our Supabase client is all set up, let’s talk about user sign-up with Supabase client-side auth in Next.js . This is where users create their accounts. We’ll need a simple form for them to enter their email and password. Let’s create a new page, say pages/signup.js .

import { useState } from 'react';
import { supabase } from '../utils/supabaseClient';
import { useRouter } from 'next/router';

export default function Signup() {
  const [email, setEmail] = useState('');
  const [password, setPassword] = useState('');
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState(null);
  const router = useRouter();

  const handleSignup = async (e) => {
    e.preventDefault();
    setLoading(true);
    setError(null);

    const { error } = await supabase.auth.signUp({
      email: email,
      password: password,
    });

    if (error) {
      setError(error.message);
    } else {
      // Redirect to a confirmation page or login page
      alert('Check your email for the confirmation link!');
      router.push('/login'); // Or wherever you want to send them
    }

    setLoading(false);
  };

  return (
    <div>
      <h1>Sign Up</h1>
      <form onSubmit={handleSignup}>
        <div>
          <label htmlFor="email">Email</label>
          <input
            id="email"
            type="email"
            value={email}
            onChange={(e) => setEmail(e.target.value)}
            required
          />
        </div>
        <div>
          <label htmlFor="password">Password</label>
          <input
            id="password"
            type="password"
            value={password}
            onChange={(e) => setPassword(e.target.value)}
            required
          />
        </div>
        <button type="submit" disabled={loading}>
          {loading ? 'Signing Up...' : 'Sign Up'}
        </button>
        {error && <p style={{ color: 'red' }}>{error}</p>}
      </form>
    </div>
  );
}

In this component, we’re using useState to manage the form inputs and loading/error states. The handleSignup function calls supabase.auth.signUp() , passing in the user’s email and password. Supabase handles the rest, including sending a confirmation email (if you have email confirmation enabled in your Supabase project settings, which you totally should!). After a successful sign-up, we’re showing an alert and then redirecting the user to the login page using useRouter from Next.js. This is a critical part of Supabase client-side auth Next.js , as it’s the first point of contact for new users. The user experience here is key, so make sure your feedback (like the alert message) is clear and helpful. We’re giving users the confidence they need to create an account. It’s all about making it super easy for them to get started!

Handling User Login

Now that users can sign up, they’ll need a way to log in, right? Let’s create a pages/login.js component for this. It’ll be quite similar to the sign-up form.

import { useState } from 'react';
import { supabase } from '../utils/supabaseClient';
import { useRouter } from 'next/router';

export default function Login() {
  const [email, setEmail] = useState('');
  const [password, setPassword] = useState('');
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState(null);
  const router = useRouter();

  const handleLogin = async (e) => {
    e.preventDefault();
    setLoading(true);
    setError(null);

    const { error } = await supabase.auth.signInWithPassword({
      email: email,
      password: password,
    });

    if (error) {
      setError(error.message);
    } else {
      // Redirect to the dashboard or a protected page
      router.push('/dashboard');
    }

    setLoading(false);
  };

  return (
    <div>
      <h1>Login</h1>
      <form onSubmit={handleLogin}>
        <div>
          <label htmlFor="email">Email</label>
          <input
            id="email"
            type="email"
            value={email}
            onChange={(e) => setEmail(e.target.value)}
            required
          />
        </div>
        <div>
          <label htmlFor="password">Password</label>
          <input
            id="password"
            type="password"
            value={password}
            onChange={(e) => setPassword(e.target.value)}
            required
          />
        </div>
        <button type="submit" disabled={loading}>
          {loading ? 'Logging in...' : 'Login'}
        </button>
        {error && <p style={{ color: 'red' }}>{error}</p>}
      </form>
    </div>
  );
}

Here, the core function is supabase.auth.signInWithPassword() . It takes the user’s credentials and attempts to log them in. Upon successful login, we redirect them to a /dashboard page. This is a fundamental part of Supabase client-side auth Next.js ; it’s how you control access to different parts of your application. Always provide clear feedback for both success and failure scenarios. A common mistake is not handling errors gracefully, which can leave users confused. We want to make sure users know exactly what’s happening with their login attempt. Trust is built on transparency, guys!

Managing User Sessions and State

Keeping track of who is logged in is crucial for Supabase client-side auth in Next.js . Supabase provides a fantastic way to manage this using session events. You can listen for changes in authentication state, such as when a user logs in or logs out.

We can set up a listener in your _app.js file to manage the user session globally. This is a common pattern in Next.js applications.

// pages/_app.js
import '../styles/globals.css';
import { useState, useEffect } from 'react';
import { supabase } from '../utils/supabaseClient';

function MyApp({ Component, pageProps }) {
  const [user, setUser] = useState(null);

  useEffect(() => {
    const { data: authListener } = supabase.auth.onAuthStateChange(
      (event, session) => {
        if (session) {
          setUser(session.user);
        } else {
          setUser(null);
        }
      }
    );

    // Fetch initial user session on mount
    supabase.auth.getSession().then(({ data: { session } }) => {
      if (session) {
        setUser(session.user);
      }
    });

    // Cleanup the listener on component unmount
    return () => {
      authListener.subscription.unsubscribe();
    };
  }, []);

  return <Component {...pageProps} user={user} />;
}

export default MyApp;

In this _app.js file, we’re using supabase.auth.onAuthStateChange . This is a real-time listener that fires whenever the authentication state changes (user logs in, logs out, session expires, etc.). We update our user state based on the session object provided by Supabase. We also fetch the initial session when the app loads to ensure the user state is correctly set. This global user state can then be passed down to any component that needs it. This is the backbone of Supabase client-side auth Next.js , ensuring your app always knows the current authentication status. Having a centralized way to manage user state means you don’t have to worry about fetching user data repeatedly across different components. It’s efficient and makes your app more responsive. Think of it as the conductor of your auth orchestra, ensuring everyone is in sync!

Implementing User Logout

Logging users out is just as important as logging them in. It’s a key part of providing a secure and user-friendly experience. Let’s add a logout button, perhaps in a navigation component or on the dashboard page.

// Example: In a Dashboard or Layout component
import { supabase } from '../utils/supabaseClient';
import { useRouter } from 'next/router';

function LogoutButton() {
  const router = useRouter();

  const handleLogout = async () => {
    const { error } = await supabase.auth.signOut();

    if (error) {
      console.error('Logout error:', error.message);
      // Handle error, maybe show a message to the user
    } else {
      // Redirect to the login page or homepage
      router.push('/login');
    }
  };

  return (
    <button onClick={handleLogout}>
      Logout
    </button>
  );
}

export default LogoutButton;

The supabase.auth.signOut() function handles the logout process. It clears the user’s session on the client and invalidates the session on the server. After a successful logout, we redirect the user to the login page. This is a fundamental aspect of Supabase client-side auth Next.js , ensuring that when a user decides to end their session, it’s done securely and completely. It’s good practice to provide some visual feedback during the logout process, even if it’s just disabling the button briefly. This confirmation reassures the user that their action has been registered. We’re cleaning up nicely here, guys!

Protecting Routes

One of the most common requirements for Supabase client-side auth in Next.js is protecting certain routes, so only logged-in users can access them. We can achieve this by creating a higher-order component (HOC) or by using Next.js’s built-in routing features in _app.js .

Let’s modify our _app.js to protect a /dashboard route. We’ll assume the user state is available from the MyApp component.

// pages/_app.js (modified)
import '../styles/globals.css';
import { useState, useEffect } from 'react';
import { supabase } from '../utils/supabaseClient';
import { useRouter } from 'next/router'; // Import useRouter

function MyApp({ Component, pageProps }) {
  const [user, setUser] = useState(null);
  const router = useRouter();
  const publicPaths = ['/', '/login', '/signup']; // Paths that don't require auth

  useEffect(() => {
    const { data: authListener } = supabase.auth.onAuthStateChange(
      (event, session) => {
        if (session) {
          setUser(session.user);
        } else {
          setUser(null);
        }
      }
    );

    supabase.auth.getSession().then(({ data: { session } }) => {
      if (session) {
        setUser(session.user);
      }
    });

    return () => {
      authListener.subscription.unsubscribe();
    };
  }, []);

  // Protect routes
  useEffect(() => {
    // If the user is not logged in and trying to access a protected route
    if (!user && !publicPaths.includes(router.pathname)) {
      router.push('/login');
    }
  }, [user, router.pathname, router]); // Add router to dependencies

  return <Component {...pageProps} user={user} />;
}

export default MyApp;

In this updated _app.js , we’ve added another useEffect hook. This hook checks if a user is logged in ( !user ) and if the current router.pathname is not in our publicPaths array. If both conditions are true, it means the user is trying to access a protected route without being logged in, so we redirect them to the /login page. This is a powerful way to implement Supabase client-side auth Next.js protection. You can expand the publicPaths array to include any pages that should be accessible to everyone. This approach ensures that sensitive data or features are only exposed to authenticated users, maintaining the integrity and security of your application. It’s like having a bouncer at your app’s exclusive party, guys!

Advanced Considerations: Email Verification and Password Reset

Supabase also offers built-in features for email verification and password resets, which are crucial for a robust authentication system. When a user signs up with supabase.auth.signUp() , Supabase can automatically send a verification email. You can configure the content and behavior of these emails in your Supabase project settings under the ‘Auth’ section.

For password resets, Supabase provides supabase.auth.resetPasswordForEmail(email) and supabase.auth.updateUser(token, { password }) . The first function sends a password reset link to the user’s email. The user clicks this link, which takes them to a page where they can enter a new password. You’ll need to handle the routing and form for this password reset process on your Next.js frontend. This involves creating a dedicated page that accepts the password reset token from the URL and allows the user to set a new password using supabase.auth.updateUser() .

These advanced features significantly enhance the security and usability of your Supabase client-side auth Next.js implementation. They provide standard, secure flows that users expect from web applications. Remember to thoroughly test these flows to ensure they work as intended and provide clear instructions to your users throughout the process. Think of these as the safety nets that catch users if they forget their password or need to verify their email – they’re essential for a smooth experience!

Conclusion

And there you have it, folks! You’ve now got a solid understanding of how to implement Supabase client-side auth in Next.js . We’ve covered setting up your Supabase client, handling user sign-up, login, logout, managing user sessions globally, and protecting your routes. Supabase makes client-side authentication incredibly accessible and powerful, especially when paired with the flexibility of Next.js.

Remember, security is paramount. Always handle sensitive information and user data with care. Keep your environment variables secure, validate user inputs, and leverage Supabase’s built-in security features. By following these steps, you can build secure, scalable, and user-friendly applications. Keep experimenting, keep building, and happy coding, guys!