You've successfully set up user authentication with Supabase Auth! Now, the crucial next step is to secure your application. This means ensuring that only authenticated users can access certain routes or view sensitive data. Supabase makes this remarkably straightforward.
At its core, protecting your routes and data involves checking the user's authentication status before granting access. Supabase provides a simple way to access the currently logged-in user's information and leverage this in your application logic.
The Supabase JavaScript client offers a convenient user object which is null if no user is authenticated, and an object containing user details if they are logged in. We can use this to conditionally render components or redirect unauthenticated users.
import { supabase } from './supabaseClient';
function ProtectedComponent() {
const [user, setUser] = React.useState(null);
React.useEffect(() => {
const { data: authListener } = supabase.auth.onAuthStateChange(
(_event, session) => {
setUser(session?.user || null);
}
);
return () => {
authListener.subscription.unsubscribe();
};
}, []);
if (!user) {
return <p>Please sign in to view this content.</p>;
}
return <p>Welcome, {user.email}! This is protected content.</p>;
}This code snippet demonstrates a common pattern: listening for authentication state changes. When the authentication state changes (e.g., user signs in or out), we update our component's user state. Then, we conditionally render the protected content only if user is not null.
Beyond frontend protection, you'll want to secure your data in Supabase itself. This is where Row Level Security (RLS) comes into play, a powerful feature that allows you to define fine-grained access control directly within your database tables.
When RLS is enabled on a table, Supabase applies policies to every database query. These policies can dictate who can SELECT, INSERT, UPDATE, or DELETE rows based on the authenticated user's identity and other conditions. Your backend code then interacts with the database as usual, and RLS ensures only permitted operations succeed.
A typical RLS policy might look like this, allowing a user to only access records where their user_id matches the user_id column in the table.
CREATE POLICY "Users can view their own data" ON "public"."todos"
FOR SELECT
USING (auth.uid() = user_id);In this example: auth.uid() is a Supabase function that returns the unique ID of the currently authenticated user. By comparing it to the user_id column in your todos table, you ensure that each user can only see their own todos. This is a fundamental security principle that prevents data leakage.
graph TD
A[User Request] --> B{Is User Authenticated?}
B -- Yes --> C[Check RLS Policies]
C -- Allowed --> D[Grant Access / Show Data]
B -- No --> E[Redirect to Login / Show Public Content]
C -- Denied --> F[Deny Access / Show Error]
This flowchart illustrates the flow of protecting your application. First, the user's authentication status is checked. If authenticated, Row Level Security policies are then consulted to determine if the requested operation is permissible. If the user is not authenticated, they are typically redirected to a login page or shown publicly accessible content.
By combining frontend checks with robust backend RLS policies, you can build secure applications where data and functionality are accessible only to the intended users, ensuring a safe and trustworthy experience for your users.