Supabase Auth: Next.js Client-Side Guide

What’s up, devs! Today we’re diving deep into a topic that’s super crucial for any modern web app: client-side authentication using Supabase with your awesome Next.js projects. Guys, getting authentication right from the get-go can save you a ton of headaches down the line, and Supabase makes it incredibly smooth, especially when you’re building with Next.js. We’ll be covering how to set up Supabase, handle user sign-ups, logins, logouts, and even how to protect your routes so only authenticated users can see certain pages. It’s all about making your app secure and user-friendly, and by the end of this, you’ll have a solid grasp on implementing this critical feature. So, grab your favorite beverage, get comfy, and let’s get this authentication party started!

Setting Up Supabase for Your Next.js App

Alright, first things first, let’s get our Supabase project ready and hooked up to our Next.js application. If you haven’t already, head over to supabase.io and create a new project. It’s free to get started, which is always a plus, guys! Once your project is created, you’ll find your Project URL and anon Key on the API page in your dashboard. Keep these handy, as you’ll need them to initialize the Supabase client in your Next.js app. To integrate Supabase into your Next.js project, the best practice is to create a dedicated client file, often named supabaseClient.js or supabase.js , typically located in a utils or lib folder. This file will be responsible for initializing the Supabase client instance using your Project URL and anon Key. This ensures that your Supabase client is configured consistently across your entire application. You can install the Supabase JavaScript client library using npm or yarn: npm install @supabase/supabase-js or yarn add @supabase/supabase-js . Inside your supabaseClient.js file, you’ll import the createClient function from the library and use your environment variables to instantiate the client. It’s super important to use environment variables (like process.env.NEXT_PUBLIC_SUPABASE_URL and process.env.NEXT_PUBLIC_SUPABASE_ANON_KEY ) to store your Supabase credentials. This keeps them secure and out of your version control. For Next.js, these environment variables need to be prefixed with NEXT_PUBLIC_ to be accessible on the client-side. So, create a .env.local file in the root of your Next.js project and add your keys there:

NEXT_PUBLIC_SUPABASE_URL=your_supabase_url
NEXT_PUBLIC_SUPABASE_ANON_KEY=your_supabase_anon_key

Then, in your supabaseClient.js :

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)

This setup ensures that your Supabase client is correctly initialized and ready to interact with your database and authentication services. It’s a foundational step that enables all the cool authentication features we’ll explore next. Remember, security is paramount , so always use environment variables for your API keys and secrets. This small step significantly enhances the security posture of your application, preventing accidental exposure of sensitive credentials.

Implementing User Sign-Up

Now that our Supabase client is set up, let’s talk about getting users signed up! This is where the magic of Supabase’s built-in authentication really shines, guys. We want to create a user-friendly sign-up form in our Next.js app. Typically, this involves a few input fields: an email and a password. We’ll capture the values from these fields and then pass them to Supabase using the signUp method. So, in your Next.js components, you’ll want to create a form that collects the user’s email and password. You’ll need state variables to manage the input values and potentially some loading and error states. When the form is submitted, you’ll prevent the default form submission behavior and call a function that handles the sign-up logic. This function will use our initialized supabase client.

Here’s a basic example of how you might structure this in a React component within your Next.js app:

import React, { useState } from 'react'
import { supabase } from '../utils/supabaseClient' // Adjust the path as needed

function SignUpForm() {
  const [email, setEmail] = useState('')
  const [password, setPassword] = useState('')
  const [loading, setLoading] = useState(false)
  const [error, setError] = useState(null)

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

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

    if (error) {
      setError(error.message)
    } else {
      // You might want to redirect the user or show a success message
      alert('Sign up successful! Please check your email to confirm.')
    }
    setLoading(false)
  }

  return (
    <form onSubmit={handleSignUp}>
      <h2>Sign Up</h2>
      <div>
        <label htmlFor="email">Email:</label>
        <input
          type="email"
          id="email"
          value={email}
          onChange={(e) => setEmail(e.target.value)}
          required
        />
      </div>
      <div>
        <label htmlFor="password">Password:</label>
        <input
          type="password"
          id="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>
  )
}

export default SignUpForm

When a user signs up, Supabase typically sends a confirmation email. This is a crucial security step to verify that the email address actually belongs to the user. You can customize these emails in your Supabase project settings. After a successful sign-up, you might want to guide the user to check their email for confirmation, or perhaps redirect them to a login page. Flexibility is key , and Supabase gives you the tools to manage this flow effectively. Remember to handle potential errors gracefully, providing clear feedback to the user if something goes wrong. This approach ensures a smooth and secure onboarding experience for your new users, building trust right from the start. The signUp method returns a user object and an error object. You’ll want to check for errors and inform the user if the sign-up failed for any reason, such as an invalid email format or a weak password. The success case often involves notifying the user to check their inbox for a confirmation link, which is a standard and recommended practice in modern authentication systems.

Handling User Login

Once users have signed up (and possibly confirmed their email), the next logical step is logging them in . This process is very similar to sign-up, but instead of signUp , we’ll use the signInWithPassword method from Supabase’s authentication module. Again, we’ll need a form for this, typically asking for the user’s email and password. Upon form submission, we’ll trigger the login function using our supabase client. The key difference here is that upon a successful login, Supabase will return the authenticated user’s session information. We need to store this session information somewhere accessible across our Next.js application so we know who is logged in and can manage their access. For client-side applications, a common pattern is to use React Context or a state management library like Redux or Zustand to store the user’s session state. This allows different components to easily access the user’s authentication status.

Here’s how you can implement a login form:

import React, { useState } from 'react'
import { supabase } from '../utils/supabaseClient' // Adjust the path as needed

function LoginForm() {
  const [email, setEmail] = useState('')
  const [password, setPassword] = useState('')
  const [loading, setLoading] = useState(false)
  const [error, setError] = useState(null)

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

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

    if (error) {
      setError(error.message)
    } else {
      // User is logged in! You can redirect them or update UI
      // The session is automatically managed by Supabase JS client
      alert('Login successful!')
      // Example: window.location.href = '/dashboard'
    }
    setLoading(false)
  }

  return (
    <form onSubmit={handleLogin}>
      <h2>Login</h2>
      <div>
        <label htmlFor="email">Email:</label>
        <input
          type="email"
          id="email"
          value={email}
          onChange={(e) => setEmail(e.target.value)}
          required
        />
      </div>
      <div>
        <label htmlFor="password">Password:</label>
        <input
          type="password"
          id="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>
  )
}

export default LoginForm

The Supabase JavaScript client automatically handles session management. When a user logs in, it stores the session details (like access tokens) in browser storage (e.g., localStorage or sessionStorage ). This means that even if the user refreshes the page, they will remain logged in. You can access the current authenticated user via supabase.auth.user() or listen for authentication state changes using supabase.auth.onAuthStateChange() . This onAuthStateChange listener is incredibly powerful for updating your UI in real-time as the user’s login status changes. For example, you can update navigation bars to show