Supabase Functions, like any backend service, often need to handle user authentication and authorization. This ensures that only legitimate users can access specific data or perform certain actions. Supabase provides powerful tools that integrate seamlessly with your Functions to manage these aspects.
The core of Supabase's authentication system is built around JWTs (JSON Web Tokens). When a user logs in or signs up, Supabase issues a JWT that contains information about the user, including their unique ID and any associated roles or permissions. This token is then typically sent to the client application, which includes it in subsequent requests to your Supabase Functions.
When a request arrives at your Supabase Function, you can access this JWT and verify its authenticity. Supabase offers built-in mechanisms to help you with this process, making it straightforward to secure your API endpoints.
Here's how you can typically access and use the user's authentication information within a Supabase Function:
import { serve } from 'https://deno.land/std@0.177.0/http/server.ts';
import { cors } from 'https://deno.land/std@0.177.0/http/middleware/cors.ts';
console.log('Functions server listening on 8000');
serve({
async handler(req) {
const headers = new Headers();
headers.set('Access-Control-Allow-Origin', '*');
headers.set('Access-Control-Allow-Headers', '*, Authorization');
if (req.method === 'OPTIONS') {
return new Response('ok', { headers });
}
// Get the JWT from the Authorization header
const authorizationHeader = req.headers.get('Authorization');
if (!authorizationHeader) {
return new Response(JSON.stringify({ error: 'Authorization header is missing' }), {
status: 401,
headers: {
'Content-Type': 'application/json',
...Object.fromEntries(headers),
},
});
}
const token = authorizationHeader.replace('Bearer ', '');
// In a real-world scenario, you would verify this token against Supabase's public keys.
// For simplicity, we're just assuming it's valid and extracting user info.
// Supabase's client libraries or Edge Functions runtime can help with token verification.
// Example: Extracting user ID from a hypothetical decoded token payload
let userId = null;
try {
// This is a placeholder for actual JWT decoding and verification
// You would use a library like 'jose' or Supabase's internal mechanisms
const decodedToken = JSON.parse(atob(token.split('.')[1])); // Basic Base64 decode for example
userId = decodedToken.sub; // 'sub' is typically the user ID
} catch (error) {
console.error('Error decoding token:', error);
return new Response(JSON.stringify({ error: 'Invalid token' }), {
status: 401,
headers: {
'Content-Type': 'application/json',
...Object.fromEntries(headers),
},
});
}
if (!userId) {
return new Response(JSON.stringify({ erIn the code above, we're extracting the Authorization header, which is expected to contain a JWT in the Bearer <token> format. While this example shows a basic extraction and a simulated decoding, in a production environment, you would need to properly verify the JWT using Supabase's public keys to ensure its integrity and prevent unauthorized access.
Supabase's Edge Functions runtime environment provides context about the authenticated user. The request.headers.get('Authorization') is the standard way to access the token. For robust JWT verification, you'd typically use a library that can fetch Supabase's public signing keys and validate the token's signature and expiration.
Authorization, on the other hand, goes beyond just knowing who the user is. It's about determining what they are allowed to do. This is often achieved by leveraging Row Level Security (RLS) policies defined in your Supabase database. Your Supabase Functions can act as intermediaries, fetching data from the database with the authenticated user's context, and RLS policies will automatically enforce access controls.
Consider this scenario: A user wants to fetch their own profile information. The client sends the JWT to your Supabase Function. The Function, using the Supabase client library, then queries the profiles table. Because the Supabase client is configured with the user's JWT (or implicitly uses the authentication context provided by the Edge Functions runtime), RLS policies on the profiles table can ensure that the query only returns rows where the id matches the authenticated user's ID.
graph TD
A[Client Application] --> B(Send JWT in Authorization Header);
B --> C{Supabase Function Endpoint};
C --> D(Extract JWT from Header);
D --> E{Verify JWT (against Supabase keys)};
E -- Valid --> F(Extract User ID);
F --> G(Interact with Supabase DB using User Context);
G --> H{RLS Policies Enforced on DB Tables};
H -- Authorized --> I[Return Data to Client];
E -- Invalid --> J[Return 401 Unauthorized];
H -- Unauthorized --> K[Return 403 Forbidden];
In summary, securing your Supabase Functions involves:
- Authentication: Verifying that a request comes from a legitimate user using JWTs.
- Authorization: Ensuring that the authenticated user has the necessary permissions to perform the requested action, often achieved through database RLS policies that your Functions interact with.
By combining the power of Supabase's authentication system with your backend logic in Functions, you can build robust, secure, and scalable APIs for your applications.