How to fix auth/invalid-provider-id: Provider ID must be supported identifier in Firebase

First, check that you're using the correct provider ID format. Firebase Authentication uses specific strings for each provider:

Common provider IDs:
- google.com (Google Sign-In)
- facebook.com (Facebook Login)
- github.com (GitHub)
- twitter.com (Twitter)
- microsoft.com (Microsoft)
- apple.com (Apple Sign-In)
- password (Email/password authentication)
- phone (Phone authentication)
- anonymous (Anonymous authentication)

Check your code for typos:

// INCORRECT - common typos
"googel.com"  // Missing 'o'
"facebok.com" // Missing 'o'
"githib.com"  // Missing 'u'
"twiter.com"  // Missing 't'

// CORRECT
"google.com"
"facebook.com"
"github.com"
"twitter.com"

Note: All OAuth providers use the .com suffix. The old format without .com (e.g., 'google') is deprecated.

Ensure the provider is enabled in your Firebase project:

1. Go to Firebase Console:
- Navigate to [Firebase Console](https://console.firebase.google.com/)
- Select your project

2. Enable authentication providers:
- In the left sidebar, click "Authentication"
- Click the "Sign-in method" tab
- You'll see a list of available providers

3. Enable each provider you need:
- Click on the provider (e.g., "Google")
- Toggle the "Enable" switch
- Fill in required configuration:
- Google: No additional config needed
- Facebook: App ID and App Secret from Facebook Developer
- GitHub: Client ID and Client Secret from GitHub OAuth Apps
- Twitter: API Key and API Secret from Twitter Developer
- Microsoft: Client ID and Client Secret from Azure AD
- Apple: Service ID, Team ID, Key ID, and Private Key

4. Save changes:
- Click "Save" after configuring each provider
- Wait a few moments for changes to propagate

Important: You must enable each provider you plan to use. Firebase won't recognize provider IDs for disabled providers.

Review your Firebase Authentication code for common mistakes:

Example: Sign in with Google (correct)

import { getAuth, signInWithPopup, GoogleAuthProvider } from "firebase/auth";

const auth = getAuth();
const provider = new GoogleAuthProvider(); // Creates provider with ID 'google.com'

signInWithPopup(auth, provider)
  .then((result) => {
    // User signed in
  })
  .catch((error) => {
    if (error.code === 'auth/invalid-provider-id') {
      console.error('Invalid provider ID:', error.message);
    }
  });

Example: Linking accounts (correct)

import { getAuth, linkWithPopup, GoogleAuthProvider } from "firebase/auth";

const auth = getAuth();
const user = auth.currentUser;
const provider = new GoogleAuthProvider();

linkWithPopup(user, provider)
  .then((result) => {
    // Account linked
  })
  .catch((error) => {
    if (error.code === 'auth/invalid-provider-id') {
      console.error('Check provider configuration');
    }
  });

Common mistakes to fix:
1. Hardcoded provider IDs: Don't pass strings directly to methods expecting provider objects
2. Incorrect method parameters: Check method signatures in Firebase documentation
3. Missing imports: Ensure you import the correct provider classes
4. Case sensitivity: Provider IDs are case-sensitive

Test your authentication flow with different providers to isolate the issue:

Create a test script:

// test-providers.js
const providers = [
  'google.com',
  'facebook.com',
  'github.com',
  'twitter.com',
  'microsoft.com',
  'apple.com',
  'password',
  'phone',
  'anonymous'
];

console.log('Testing provider IDs:');
providers.forEach(provider => {
  console.log(`  ${provider} - ${isValidProvider(provider) ? 'VALID' : 'INVALID'}`);
});

// Simulate Firebase validation
function isValidProvider(providerId) {
  const validProviders = [
    'google.com', 'facebook.com', 'github.com', 'twitter.com',
    'microsoft.com', 'apple.com', 'password', 'phone', 'anonymous'
  ];
  return validProviders.includes(providerId);
}

Test in your app:
1. Start with Google provider (simplest to configure)
2. If Google works, test other providers one by one
3. Note which providers fail and check their Firebase Console configuration
4. Compare working vs non-working provider configurations

Debug tips:
- Use browser developer tools to inspect network requests
- Check Firebase Console > Authentication > Events for errors
- Enable debug logging in Firebase: firebase.auth().setPersistence(firebase.auth.Auth.Persistence.NONE)

If you're using custom authentication, ensure proper configuration:

Custom provider setup:

// Custom authentication provider example
import { getAuth, signInWithCustomToken } from "firebase/auth";

const auth = getAuth();

// Your backend should generate custom tokens
async function signInWithCustomProvider(userId) {
  // Call your backend to get a custom token
  const response = await fetch('/api/auth/custom-token', {
    method: 'POST',
    body: JSON.stringify({ userId })
  });

  const { customToken } = await response.json();

  // Sign in with the custom token
  signInWithCustomToken(auth, customToken)
    .then((userCredential) => {
      // Signed in
    })
    .catch((error) => {
      if (error.code === 'auth/invalid-provider-id') {
        console.error('Custom token issue:', error);
      }
    });
}

Common custom auth issues:
1. Invalid custom tokens: Tokens must be properly signed with your Firebase service account
2. Token expiration: Custom tokens expire after 1 hour
3. Service account permissions: Ensure your service account has Firebase Authentication Admin permissions
4. Token claims: Custom claims must be valid JSON

Verify custom token generation:

// Server-side token generation (Node.js)
const admin = require('firebase-admin');

admin.initializeApp({
  credential: admin.credential.cert(serviceAccount),
});

const customToken = await admin.auth().createCustomToken(uid, {
  customClaim: 'value'
});

Ensure you're using compatible Firebase SDK versions:

Check Firebase SDK version:

// package.json
{
  "dependencies": {
    "firebase": "^10.0.0",  // Check for latest version
    // or for modular SDK:
    "firebase-auth": "^1.0.0"
  }
}

Update Firebase SDK:

# For npm
npm update firebase

# For yarn
yarn upgrade firebase

# For specific modular packages
npm update firebase-auth firebase-app

Check for breaking changes:
1. Review Firebase release notes: [Firebase Release Notes](https://firebase.google.com/support/release-notes)
2. Look for provider ID changes: Some provider IDs have changed between versions
3. Check migration guides: If upgrading from v8 to v9 (modular SDK)

Version compatibility:
- Firebase JavaScript SDK v9+ uses modular imports
- Provider IDs are consistent across v8 and v9
- Some deprecated methods may have different parameter requirements

Test after update:
1. Clear node_modules and reinstall: rm -rf node_modules && npm install
2. Test authentication with a simple provider (Google)
3. Gradually test other providers