Android Example Firebase Phone Authentication in B4A using WebView + WebServer (Working Example)

Firebase Phone Authentication in B4A using WebView + WebServer (Step-by-Step Setup)​

This example shows how to implement Firebase Phone Authentication in B4A using a WebView + remote WebServer instead of a native Firebase Phone library.

I was forced to look for an alternative solution because the Firebase Phone Auth library I was previously using is currently not compatible with the latest version of B4A. After testing different approaches, I found this simple and stable method, which might help others facing the same issue.
Below are the steps to make it work.

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1) Load the B4A Example Project​

First, download and open the provided B4A example project.
The example:

• Opens a WebView
• Loads the authentication page from your server
• Waits for the result (OK / ERROR)
• Continues the login flow inside the app

⚠ Important:
Inside the class FirebaseAuthPhoneWeb you must set the URL of your own webserver.

Dim url As String = "https://www.domain.com/urlphoneauth"

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2) Upload the WebServer Files to Your Server​

You must upload the required web files to your hosting/server.

Create a folder on your server, for example:

https://www.domain.com/firebaseauth/

Inside that folder upload these files (from the webserver folder in the example):

• index.php
• verify.php
• styles.php

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3) Configure Firebase in index.php​

Open index.php and complete the Firebase configuration block with your real project credentials:

// --- Firebase config ---
const firebaseConfig = {
  apiKey: "<?php echo $firebase_auth_apiKey; ?>",
  authDomain: "<?php echo $firebase_auth_authDomain; ?>",
  projectId: "<?php echo $firebase_auth_projectId; ?>",
  appId: "<?php echo $firebase_auth_appId; ?>"
};

Make sure these PHP variables are properly defined (for example in a config section or at the top of the file).
You can get these values from:
Firebase Console → Project Settings → General → Your Apps

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4) Update the fetch() URL to Your Domain​

Inside index.php, locate this line:
const res = await fetch('https://www.domain.com/firebaseauth/verify.php'
Replace www.domain.com with your real domain.

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5) Install Firebase PHP SDK (kreait/firebase-php)​

On your server, inside the same folder where index.php and verify.php are located, run:
composer.phar require kreait/firebase-php
This will generate:

• composer.json
• composer.lock
• vendor/ folder

The vendor folder is required for verify.php to work.

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6) Download and Add service-account.json​

From Firebase Console:
Project Settings → Service Accounts → Generate new private key
Download the file (usually called):
service-account.json
It contains fields like:

• project_id
• private_key_id
• private_key
• client_email

Place this file in your webserver folder (or wherever your verify.php expects it).
⚠ Do NOT upload this file to public repositories.

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7) Test Firebase Phone Authentication (Real SMS)​

Once everything is configured:

• Web files uploaded
• Firebase config added
• Composer installed
• vendor/ present
• service-account.json added

You can run the B4A example.

Firebase will:

• Send a real SMS
• Validate the OTP
• Return the authentication result to your app

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Debug Mode in the B4A Example​

In the B4A example, I added a debug parameter to avoid getting blocked due to too many verification attempts.
The URL is built like this:
urlphoneauth = url & "?debug=1&rid=" & rid
When debug=1 is enabled, you can safely test the flow without triggering too many real SMS requests (depending on your server-side implementation).

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Using Test Phone Numbers in Firebase (No Real SMS Needed)​

Firebase allows you to configure test phone numbers with predefined verification codes.
In Firebase Console:
Authentication → Sign-in method → Phone → Add test phone number
Example used in the demo:

• Test phone number: 666555444
• Verification code: 665544

This allows you to test the full flow without sending real SMS messages.

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If anyone needs improvements or wants to adapt it to a fully WebServer (embedded in the device), feel free to ask.
Hope this helps others facing Firebase Phone Auth issues in B4A