How do I resolve CSP errors with Firebase popup authentication in a Chrome extension?

Below is a summary of the recommendations to try:

Use Offscreen Documents Instead of Relying on a Direct Popup

Manifest V3 imposes stricter restrictions on how code from external sources can be loaded. Instead of opening a popup directly (which will be blocked by Chrome extensions), the recommended approach is to use an offscreen document. An offscreen document acts as a proxy by loading your hosted authentication page inside an iframe, then relaying the authentication result using postMessage.

Ensure OAuth Domains Are Authorized in the Firebase Console

For federated sign‑in (e.g., Google or GitHub), add your extension’s Chrome URL (e.g. chrome-extension://<YOUR_EXTENSION_ID>) as an authorized domain in your Firebase Console (under Authentication → Settings). Without this, the OAuth flow won’t work.

Adjust Your Content Security Policy Appropriately

Verify that your Content Security Policy (CSP) includes every URL needed by the authentication providers. For instance, include these in your CSP allowlist (in addition to what you already have):

JSONCopied
"connect-src": "'self' https://apis.google.com https://www.gstatic.com https://www.googleapis.com https://identitytoolkit.googleapis.com https://accounts.google.com https://*.google.com"

You may also need to include the URLs for secure tokens and any additional endpoints that Firebase Authentication uses.

Use the firebase/auth/web-extension Entry Point

When building the authentication flow for a Chrome extension, use the provided firebase/auth/web-extension entry point. This makes your code similar to a web app:

JSCopied
import { getAuth, signInWithPopup, GoogleAuthProvider } from 'firebase/auth/web-extension';
import { initializeApp } from 'firebase/app';
import firebaseConfig from './firebaseConfig.js';

const app = initializeApp(firebaseConfig);
const auth = getAuth();

const provider = new GoogleAuthProvider();

signInWithPopup(auth, provider)
  .then((userCredential) => {
    // Process the authenticated user here.
    const user = userCredential.user;
    console.log('User authenticated:', user);
  })
  .catch((error) => {
    console.error('Authentication error:', error);
  });

Recap of What to Do

1. Use Offscreen Documents:

   • Create an offscreen page that loads your Firebase‑hosted auth page in an iframe.
   • In that offscreen document, wrap your authentication logic and forward the results via postMessage.

2. Authorize Your Extension’s Domain:

   • Add chrome-extension://<YOUR_EXTENSION_ID> to your authorized domains in the Firebase Console.

3. Update Your CSP:

   • Double-check that all necessary domains (e.g. to Google APIs and Firebase endpoints) are included in the connect-src directive.
   • Include the OAuth providers’ endpoints (e.g. https://apis.google.com, https://securetoken.googleapis.com, etc.).

4. Use the Correct Firebase Auth Import:

   • Use firebase/auth/web-extension when running code from within your offscreen document or extension iframe.

With these adjustments, your popup-based authentication flow will be implemented via an offscreen document in the extension, ensuring that the CSP is met and external code loads properly.