Table of contents

Quick Summary:

In this blog, we address Firebase OTP auto-read issues on Android 13+ caused by stricter security policies, background restrictions, and limited SMS access. Older implementations relying solely on startOtpListener often fail, leading to invalid OTP errors. To ensure seamless authentication, we propose a robust solution combining auto-read functionality, Firebase’s onAuthStateChanged fallback, and manual OTP entry as a backup. This approach enhances reliability across all Android versions while maintaining compliance with new security updates.


Introduction

Firebase OTP authentication enhances user experience by enabling automatic phone number verification. However, with Android 13 and newer versions, stricter security policies have made OTP auto-read unreliable. Background restrictions, limited SMS access, and changes in app lifecycle management often cause failures, requiring alternative approaches.

For those working with Firebase in React Native app development, these challenges can significantly impact authentication flows. In this blog, we’ll explore why OTP auto-read fails on higher Android versions, analyze common issues in previous implementations, and present a robust solution to ensure seamless OTP verification across all devices.


Why Does OTP Auto-Read Fail on Higher Android Versions?

With Android’s recent updates, particularly versions 13 and above, several security enhancements have been introduced that affect the functionality of the SMS Retriever API, which Firebase relies on for OTP auto-reading. These changes include:

  1. Stricter Background Restrictions: Modern Android versions impose stricter limitations on background tasks, often causing the OTP listener to be interrupted.
  2. Limited SMS Access: Apps now require explicit permissions to access SMS messages. Even with permissions, compliance with newer app policies is necessary.
  3. App Lifecycle Management: The app lifecycle management in Android 13+ may pause or kill background listeners, interrupting OTP auto-read functionality.

Due to these restrictions, users on newer Android versions may encounter invalid OTP errors, or the auto-read feature may not trigger at all. This results in a less seamless experience as users have to manually input OTPs.


A Common Problem with Previous Implementations

In earlier implementations, developers often relied solely on the startOtpListener method from libraries like react-native-otp-verify. While this worked well on older Android versions, issues arose on Android 13+ where OTPs were sometimes marked invalid or auto-verified in the background without the user’s knowledge. Here’s an example of such a problematic implementation:

ExampleCode: SignUpScreen.tsx

useEffect(() => {
  if (currentPage === SCREEN.OTP && !IS_IOS) {
    try {
      setTimeout(() => {
        startOtpListener(async (message: any) => {
          // Extract the OTP using regex
          const otp = await message.match(/\b\d{6}\b/)[0];
          verifiedOTP(otp);
        }).catch((error: any) => {
          Alert.alert('Error', error?.message);
        });
        return () => removeListener();
      }, 1500);
    } catch (error: any) {
      Alert.alert('Error', error?.message);
    }
  }
}, [currentPage]);
const phoneContinue = async () => {
  setLoading(true);
  try {
    const confirmation = await auth().signInWithPhoneNumber(`+91${phoneNumber}`);
    setConfirm(confirmation?.verificationId);
    setLoading(false);
    setCurrentPage(SCREEN.OTP);
  } catch (error: any) {
    setLoading(false);
    Alert.alert('Error', error?.message);
    console.log('Error', error);
  } finally {
    setLoading(false);
  }
};

This implementation fails on higher Android versions due to background interruptions and incorrect OTP verification triggered by the auto-read process.


The Solution

To overcome these challenges, it’s essential to implement a fallback mechanism. By combining Firebase’s onAuthStateChanged listener with an OTP auto-read library like react-native-otp-verify, you can ensure reliable authentication across all Android versions. This approach involves:

  1. Auto-Read Functionality: Leveraging startOtpListener for automatic OTP detection.
  2. Fallback Listener: Using Firebase’s onAuthStateChanged to detect successful logins, even when auto-read fails.
  3. Manual Entry Support: Allowing users to manually enter the OTP if both mechanisms fail.

Improved Implementation

Here’s an example of how to handle OTP authentication reliably with both auto-read and fallback mechanisms:

Example Code: SignUpScreen.tsx

import { useEffect, useState } from 'react';
import { Alert, TextInput, SafeAreaView, View, Text, TouchableOpacity } from 'react-native';
import auth from '@react-native-firebase/auth';
import { startOtpListener, removeListener } from 'react-native-otp-verify';
const SCREEN = { PHONE_NO: 'PHONE_NO', OTP: 'OTP' };
const SignUp = () => {
  const [phoneNumber, setPhoneNumber] = useState('');
  const [otp, setOtp] = useState('');
  const [confirm, setConfirm] = useState(null);
  const [currentPage, setCurrentPage] = useState(SCREEN.PHONE_NO);
  useEffect(() => {
    if (currentPage === SCREEN.OTP) {
      try {
        startOtpListener((message) => {
          const extractedOtp = message.match(/\b\d{6}\b/)[0];
          setOtp(extractedOtp);
          verifyOtp(extractedOtp);
        });
      } catch (error) {
        console.error('Error in OTP listener:', error);
        Alert.alert('Error', 'Failed to auto-read OTP. Please enter it manually.');
      }
      return () => removeListener();
    }
  }, [currentPage]);
  useEffect(() => {
    if (currentPage === SCREEN.OTP) {
      const subscriber = auth().onAuthStateChanged((user) => {
        if (user) {
          console.log('User authenticated:', user);
        }
      });
      return subscriber;
    }
  }, [currentPage]);
  const sendOtp = async () => {
    try {
      const confirmation = await auth().signInWithPhoneNumber(`+91${phoneNumber}`);
      setConfirm(confirmation);
      setCurrentPage(SCREEN.OTP);
    } catch (error) {
      Alert.alert('Error', 'Failed to send OTP. Please try again.');
      console.error(error);
    }
  };
  const verifyOtp = async (incomingOtp) => {
    try {
      const credential = auth.PhoneAuthProvider.credential(confirm.verificationId, incomingOtp);
      await auth().signInWithCredential(credential);
    } catch (error) {
      Alert.alert('Error', 'Invalid OTP. Please try again.');
      console.error(error);
    }
  };
  return (
    <SafeAreaView>
      {currentPage === SCREEN.PHONE_NO ? (
        <View>
          <Text>Enter Phone Number:</Text>
          <TextInput
            value={phoneNumber}
            onChangeText={setPhoneNumber}
            keyboardType="phone-pad"
            placeholder="Enter phone number"
          />
          <TouchableOpacity onPress={sendOtp}>
            <Text>Send OTP</Text>
          </TouchableOpacity>
        </View>
      ) : (
        <View>
          <Text>Enter OTP:</Text>
          <TextInput
            value={otp}
            onChangeText={setOtp}
            keyboardType="numeric"
            placeholder="Enter OTP"
          />
          <TouchableOpacity onPress={() => verifyOtp(otp)}>
            <Text>Verify OTP</Text>
          </TouchableOpacity>
        </View>
      )}
    </SafeAreaView>
  );
};
export default SignUp;

How This Works

1. Auto-Read Mechanism: The startOtpListener method monitors incoming SMS messages, extracts the OTP using regex, and triggers automatic verification. This reduces the need for manual input.

2. Fallback Using Auth State Listener: Firebase’s onAuthStateChanged ensures that if the auto-read mechanism fails, successful OTP verification updates the user’s authentication state, acting as a reliable backup.

3. Manual Entry as a Backup: For scenarios where both mechanisms fail, users can still manually input the OTP, ensuring the authentication process remains functional.

Conclusion

By integrating Firebase’s onAuthStateChanged listener with a robust OTP auto-read mechanism, developers can overcome the challenges introduced by Android’s modern security policies. This ensures a seamless and reliable authentication experience, regardless of the Android version.

For businesses building secure mobile applications, it’s crucial to adapt to these changes. If implementing these solutions seems complex, hiring React Native developers with expertise in Firebase authentication can help streamline the process. Experienced developers can optimize OTP workflows, ensuring compliance with Android’s evolving security standards while enhancing user experience.


React Native
Yash Nayi
Yash Nayi

Software Engineer

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