Great question! You don’t have to fully eject from Expo to add Firebase phone authentication to your React Native app. Here are practical, production-ready approaches, plus a look at whether the iframe idea works:

1. Use Expo Prebuild (Recommended) #

Expo Prebuild lets you convert your Expo project into a native project structure while keeping the Expo development workflow intact. This unlocks full access to Firebase Auth’s native SDK, including phone authentication:

• First, install the required dependencies:

  npx expo install expo-firebase-app expo-firebase-auth
  

• Run npx expo prebuild to generate native iOS and Android project files
• Follow Firebase’s official docs to configure platform-specific settings: add SHA-1 fingerprints to your Firebase project, update Info.plist (iOS) and AndroidManifest.xml (Android) with auth-related permissions
• You can then use Firebase Auth’s phone auth APIs just like in a standard React Native app:

  import { getAuth, signInWithPhoneNumber } from 'expo-firebase-auth';
  
  const handlePhoneSignIn = async (phoneNumber) => {
    const auth = getAuth();
    try {
      const confirmation = await signInWithPhoneNumber(auth, phoneNumber);
      // Store confirmation.verificationId to use with the entered code
      return confirmation;
    } catch (error) {
      console.error('Phone sign-in error:', error);
    }
  };
  

2. Use Expo Dev Client #

If you don’t want to generate native project files upfront, Expo Dev Client lets you build a custom development app that supports native modules. This way you can test phone auth without ejecting:

• Build your custom Dev Client with:

  npx expo run:ios  # For iOS
  npx expo run:android  # For Android
  

• Launch your project in the custom Dev Client instead of Expo Go, and you’ll have full access to Firebase’s phone authentication features

What About Embedding an Iframe with Firebase Web UI? #

While technically possible using a WebView component like expo-webview, this approach is not recommended for production apps:

• Poor user experience: WebView-based auth feels disjointed from your native app—keyboard handling, navigation, and loading states won’t match native behavior
• Security risks: Passing authentication tokens between the WebView and your native app requires careful handling to avoid leaks or XSS vulnerabilities
• Maintenance overhead: You’ll have to maintain a separate web-based auth flow alongside your native app, which adds complexity

Sticking with Expo Prebuild or Dev Client is the better choice—you get the best of both worlds: Expo’s streamlined development experience and full access to Firebase’s native auth tools.

内容的提问来源于stack exchange，提问作者dor.elmaliach