Google Sign In Setup Guide for Mobile App

This guide will help you set up Google Sign In in your MartFury mobile app.

Prerequisites

1. A Google Cloud Platform Account
2. A Firebase project (recommended) or standalone Google Cloud project
3. Basic knowledge of mobile app development

Step 1: Configure Google Cloud Platform

Option A: Using Firebase (Recommended)

1. Go to Firebase Console
2. Create a new project or select an existing one
3. Add your Android and iOS apps to the project
4. Download configuration files:
   • Android: google-services.json → place in android/app/
   • iOS: GoogleService-Info.plist → place in ios/Runner/

Option B: Using Google Cloud Console

1. Go to Google Cloud Console
2. Create a new project or select an existing one
3. Go to APIs & Services → Credentials
4. Click Create Credentials → OAuth client ID

Step 2: Create OAuth 2.0 Client IDs

You need to create multiple OAuth client IDs:

Web Client ID (Required)

1. In Google Cloud Console → Credentials → Create OAuth client ID
2. Application type: Web application
3. Name: MartFury Web Client
4. Click Create
5. Copy the Client ID - this is your GOOGLE_CLIENT_ID

iOS Client ID (Required for iOS)

1. Create OAuth client ID → Application type: iOS
2. Bundle ID: Your app's bundle identifier (e.g., com.yourcompany.martfury)
3. Click Create
4. Copy the iOS URL scheme (format: com.googleusercontent.apps.XXXX)

Android Client ID (Required for Android)

1. Create OAuth client ID → Application type: Android
2. Package name: Your app's package name (e.g., com.yourcompany.martfury)
3. SHA-1 certificate fingerprint:

   # For debug keystore
   keytool -list -v -keystore ~/.android/debug.keystore -alias androiddebugkey -storepass android -keypass android
   
   # For release keystore
   keytool -list -v -keystore your-release-key.keystore -alias your-alias

4. Click Create

SHA-1 Fingerprint

You need separate Android OAuth clients for debug and release builds, each with their respective SHA-1 fingerprints.

Step 3: Configure Your Mobile App

Environment Variables

Create or update your .env file:

# Google Sign-In credentials
# Use the Web Client ID (not iOS or Android client IDs)
GOOGLE_CLIENT_ID=your-web-client-id.apps.googleusercontent.com
GOOGLE_SERVER_CLIENT_ID=your-web-client-id.apps.googleusercontent.com

# Enable Google Sign-In
ENABLE_GOOGLE_SIGN_IN=true

Variable	Description
GOOGLE_CLIENT_ID	Web application OAuth client ID
GOOGLE_SERVER_CLIENT_ID	Same as above (used for backend verification)

iOS Configuration

Update your ios/Runner/Info.plist to include the reversed client ID as a URL scheme:

<key>CFBundleURLTypes</key>
<array>
    <dict>
        <key>CFBundleTypeRole</key>
        <string>Editor</string>
        <key>CFBundleURLSchemes</key>
        <array>
            <!-- Add your reversed iOS client ID here -->
            <string>com.googleusercontent.apps.YOUR_IOS_CLIENT_ID</string>
        </array>
    </dict>
</array>

Finding Your Reversed Client ID

The reversed client ID is provided in Google Cloud Console when you create the iOS OAuth client. It looks like: com.googleusercontent.apps.123456789-abcdefg

Android Configuration

The google_sign_in Flutter package handles Android configuration automatically. Ensure you have:

1. google-services.json in android/app/ (if using Firebase)
2. SHA-1 fingerprint registered in Google Cloud Console

No manual AndroidManifest.xml changes are required.

Step 4: Configure OAuth Consent Screen

1. Go to Google Cloud Console → APIs & Services → OAuth consent screen
2. Choose External user type (or Internal for organization apps)
3. Fill in required fields:
   • App name
   • User support email
   • Developer contact email
4. Add scopes: email, profile, openid
5. Add test users if app is in testing mode
6. Submit for verification (for production)

Step 5: Testing the Integration

1. Run your app
2. Go to the login screen
3. Tap the Google Sign In button
4. Select a Google account
5. Verify that you're redirected back to your app

Troubleshooting

Common Issues

1. Google Sign In button not showing

• Verify ENABLE_GOOGLE_SIGN_IN=true in your .env file
• Ensure both GOOGLE_CLIENT_ID and GOOGLE_SERVER_CLIENT_ID are set
• Restart the app completely (hot reload doesn't apply .env changes)

2. "Sign In failed" or "ApiException: 10"

This usually means configuration mismatch:

• iOS: Verify the reversed client ID is in Info.plist URL schemes
• Android: Verify SHA-1 fingerprint matches your keystore
• Check that package name/bundle ID matches OAuth client configuration

3. "DEVELOPER_ERROR" on Android

• SHA-1 fingerprint mismatch - regenerate and update in Google Cloud Console
• Package name mismatch between app and OAuth client
• Missing google-services.json file

4. Sign In works but backend rejects token

• Ensure GOOGLE_SERVER_CLIENT_ID matches the Web client ID
• Backend must be configured to verify tokens with the same client ID

5. "User cancelled sign-in"

• User tapped outside the account picker or pressed back
• This is expected behavior, not an error

Getting Help

If you encounter any issues:

1. Check the Google Sign-In Documentation
2. Review the google_sign_in package documentation
3. Check your app's logs for detailed error messages

Security Considerations

1. Never commit your Google Client IDs to version control
2. Always use environment variables for sensitive data
3. Implement proper error handling and user feedback
4. Verify tokens on your backend before trusting them

Additional Resources

• Google Cloud Console
• Firebase Console
• Google Sign-In Documentation
• google_sign_in Package