Firebase Google Sign-In Demo (Android + Backend)

This project is a comprehensive, full-stack demonstration of how to implement Google Sign-In in an Android application with a secure backend verification system. It showcases the modern approach using Android's Credential Manager API and a Node.js (Express) backend to validate Google ID tokens.

The primary goal is to provide a clear, end-to-end example of a secure authentication flow, from the user tapping the "Sign in with Google" button on their device to the backend server verifying their identity and issuing a session token.

Demo

Project Structure

The repository is organized into two main parts:

• ./android: Contains the native Android application built with Kotlin. It handles the user interface, Google Sign-In flow via Credential Manager, and communication with the backend.
• ./backend: Contains the Node.js (Express) server built with TypeScript. It exposes an API endpoint to verify Google ID tokens and issue custom JWTs for session management.

Features

• Android Client (using Credential Manager):
  • Modern, simplified Google Sign-In implementation.
  • Login screen with a "Sign in with Google" button.
  • Profile screen to display user information after successful login.
  • Securely sends the Google ID token to the backend.
• Node.js Backend:
  • Verifies the integrity and authenticity of Google ID tokens.
  • Issues custom JSON Web Tokens (JWTs) to the client for session management.
  • Built with Express.js and TypeScript for a robust and scalable setup.

Technologies Used

• Frontend (Android):
  • Kotlin
  • Firebase Authentication
  • Google Sign-In with Credential Manager API
• Backend:
  • Node.js with Express.js
  • TypeScript
  • Bun (runtime and package manager)
  • JSON Web Tokens (JWT)
  • Google Auth Library

Getting Started

To run this demo, you need to set up a Firebase project, configure the backend, and then run the Android application.

1. Firebase Project Setup (Required for both Android and Backend)

Follow the detailed instructions in the Android README to:

1. Create a Firebase project.
2. Add your Android app to the project.
3. Enable the Google Sign-In provider.
4. Add your SHA-1 fingerprint.
5. Crucially, obtain your Web Client ID, which is needed for both the Android app and the backend.

2. Backend Setup

1. Navigate to the backend directory.
2. Follow the instructions in the backend README to install dependencies and create your .env file.
3. Start the backend server:

   cd backend
   bun run dev

   The server will be running at http://localhost:3000.

3. Android App Setup

1. Follow the instructions in the Android README to add your Web Client ID to the project.
2. Set up a reverse proxy to allow the app to communicate with your local backend:

   # Make sure your Android device is connected or emulator is running
   adb reverse tcp:3000 tcp:3000

3. Build and run the app on your Android device or emulator.

Detailed Documentation

For more detailed information on each part of the project, please refer to their respective README files:

• Android README
• Backend README