Mohammad Shaker
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Per-App Social Authentication: Selective Sign-In Strategy

·auth-security

Per-App Social Authentication: Selective Sign-In Strategy

Not all apps are ready for social authentication at the same time. Rolling out Google and Apple Sign-In uniformly across Amal, Thurayya, and Ilham would have introduced authentication complexity in apps not yet prepared for it. We implemented per-app feature flags to enable selective social authentication rollout.

The Problem

We completed Google OAuth integration, but only Amal was ready for launch. Thurayya and Ilham required additional frontend work, legal review, and user testing. A global authentication switch would have forced premature launches.

Risk of forced rollout:

  • Incomplete mobile UI flows
  • Untested edge cases in production
  • Legal compliance issues (data processing agreements not finalized)
  • Support team unprepared for authentication questions

Architecture: Before vs After

Before:

All Apps Enabled
┌──────────────────┐
│ Amal App         │ ← Google Sign-In ON
├──────────────────┤
│ Thurayya App     │ ← Google Sign-In ON
├──────────────────┤
│ Ilham App        │ ← Google Sign-In ON
└──────────────────┘
    Same config for all apps

After:

Selective Enablement
┌──────────────────┐
│ Amal App         │ ← Google + Apple ON
├──────────────────┤
│ Thurayya App     │ ← Social Sign-In OFF
├──────────────────┤
│ Ilham App        │ ← Social Sign-In OFF
└──────────────────┘
    Per-app feature flags

Request Flow

When a mobile app requests authentication endpoints, the backend checks per-app configuration:

Authentication Request Flow
┌──────────────────┐       ┌──────────────────┐       ┌──────────────────┐
│ Mobile App       │──────>│ API Gateway      │──────>│ Flask Backend    │
│ - app_name       │       │ - Route to auth  │       │ - Check config   │
│ - auth method    │       │   endpoints      │       │ - Return enabled │
└──────────────────┘       └──────────────────┘       │   methods        │
                                                       └──────────────────┘

Request: GET /auth/methods?app=amal
Response: {
  "google": true,
  "apple": true,
  "email": true
}

Request: GET /auth/methods?app=thurayya
Response: {
  "google": false,
  "apple": false,
  "email": true
}

Implementation Details

Configuration Structure

We used a nested dictionary in src/bootstrap_stages/ to define per-app authentication methods:

SOCIAL_AUTH_CONFIG = {
    "amal-app": {
        "google_enabled": True,
        "apple_enabled": True,
        "google_client_id": "amal-google-client-id",
        "apple_client_id": "amal-apple-client-id",
    },
    "thurayya-app": {
        "google_enabled": False,
        "apple_enabled": False,
        "google_client_id": None,
        "apple_client_id": None,
    },
    "ilham-app": {
        "google_enabled": False,
        "apple_enabled": False,
        "google_client_id": None,
        "apple_client_id": None,
    }
}

API Endpoint for Feature Discovery

Mobile apps need to know which authentication methods are available:

@auth_blueprint.route('/methods', methods=['GET'])
def get_auth_methods():
    """Return enabled authentication methods for requesting app."""
    app_name = request.args.get('app')

    if not app_name:
        return {"error": "app parameter required"}, 400

    config = SOCIAL_AUTH_CONFIG.get(app_name, {})

    return {
        "google": config.get("google_enabled", False),
        "apple": config.get("apple_enabled", False),
        "email": True,  # Always available
        "phone": True   # Always available
    }

Conditional Route Registration

Authentication routes register conditionally based on app configuration:

def register_auth_routes(app, app_name):
    """Register authentication routes based on app configuration."""
    config = SOCIAL_AUTH_CONFIG.get(app_name, {})

    # Always register email/phone authentication
    app.register_blueprint(email_auth_blueprint)
    app.register_blueprint(phone_auth_blueprint)

    # Conditionally register social authentication
    if config.get("google_enabled"):
        app.register_blueprint(google_auth_blueprint)

    if config.get("apple_enabled"):
        app.register_blueprint(apple_auth_blueprint)

Mobile App Integration

Mobile apps query the /auth/methods endpoint at startup:

// Swift (iOS)
func fetchAuthenticationMethods() async {
    let url = URL(string: "\(apiBase)/auth/methods?app=amal")!
    let (data, _) = try await URLSession.shared.data(from: url)
    let methods = try JSONDecoder().decode(AuthMethods.self, from: data)

    // Update UI based on available methods
    showGoogleButton = methods.google
    showAppleButton = methods.apple
}

// Kotlin (Android)
suspend fun fetchAuthenticationMethods(): AuthMethods {
    val response = httpClient.get("$apiBase/auth/methods?app=amal")
    return response.body<AuthMethods>()
}

Rollout Strategy

We implemented a phased rollout across apps:

Phase 1: Amal (Week 1)

  • Enable Google and Apple Sign-In
  • Monitor error rates and authentication success
  • Gather user feedback
  • Fix bugs in authentication flow

Phase 2: Thurayya (Week 4)

  • Apply lessons learned from Amal
  • Enable Google Sign-In only (Apple pending legal review)
  • Monitor cross-app authentication patterns

Phase 3: Ilham (Week 8)

  • Full social authentication rollout
  • All authentication methods enabled
  • Unified authentication experience

This staged approach allowed us to:

  • Test in production with smaller user base
  • Fix bugs before wider rollout
  • Prepare support team incrementally
  • Complete legal reviews per app

Benefits of Per-App Configuration

1. Risk Mitigation

Bugs in social authentication affected only enabled apps. When we discovered a Google token validation issue in Amal, Thurayya and Ilham were unaffected.

2. A/B Testing

We compared authentication conversion rates:

  • Amal (with social auth): 68% sign-up completion
  • Thurayya (email only): 52% sign-up completion

This 16-percentage-point difference justified investing in social authentication for all apps.

3. Legal Compliance

Apple Sign-In requires specific data processing agreements. Per-app flags let us launch Google first while completing Apple legal reviews.

4. Independent Development Velocity

Amal mobile team completed social auth UI before Thurayya. Per-app flags prevented blocking Amal's launch while Thurayya caught up.

Configuration Management

Environment-Specific Configuration

Configuration varies by environment:

# Development
SOCIAL_AUTH_CONFIG = {
    "amal-app": {"google_enabled": True, "apple_enabled": True},
    "thurayya-app": {"google_enabled": True, "apple_enabled": True},  # Test all features
    "ilham-app": {"google_enabled": True, "apple_enabled": True},
}

# Production
SOCIAL_AUTH_CONFIG = {
    "amal-app": {"google_enabled": True, "apple_enabled": True},
    "thurayya-app": {"google_enabled": False, "apple_enabled": False},  # Not ready
    "ilham-app": {"google_enabled": False, "apple_enabled": False},
}

Dynamic Configuration (Future)

We designed the system to support database-backed feature flags:

def get_auth_config(app_name):
    """Fetch auth configuration from database (future feature)."""
    config = FeatureFlag.query.filter_by(
        app_name=app_name,
        feature_type='authentication'
    ).first()

    return config.to_dict() if config else DEFAULT_CONFIG

This enables runtime configuration changes without redeployment.

Testing Strategy

Unit Tests

We tested per-app configuration logic:

def test_auth_methods_amal_enabled():
    """Amal should have all auth methods enabled."""
    response = client.get('/auth/methods?app=amal-app')
    assert response.json['google'] is True
    assert response.json['apple'] is True

def test_auth_methods_thurayya_disabled():
    """Thurayya should have social auth disabled."""
    response = client.get('/auth/methods?app=thurayya-app')
    assert response.json['google'] is False
    assert response.json['apple'] is False

Integration Tests

We verified end-to-end authentication flows per app:

def test_google_auth_amal_success():
    """Google authentication should succeed for Amal."""
    response = client.post('/auth/google/callback', json={
        'app': 'amal-app',
        'code': 'valid-oauth-code'
    })
    assert response.status_code == 200

def test_google_auth_thurayya_disabled():
    """Google authentication should fail for Thurayya."""
    response = client.post('/auth/google/callback', json={
        'app': 'thurayya-app',
        'code': 'valid-oauth-code'
    })
    assert response.status_code == 403
    assert 'not enabled' in response.json['error']

Results

Before implementation:

  • All-or-nothing authentication rollout
  • High risk of production issues
  • Blocked by slowest app's readiness

After implementation:

  • Strategic per-app rollout (1 app → 2 apps → 3 apps over 8 weeks)
  • Zero cross-app authentication bugs
  • 16% higher sign-up conversion in apps with social auth
  • Legal compliance maintained per app

Engineering metrics:

  • 0 production incidents from premature rollouts
  • 3 separate launch dates (reduced coordination overhead)
  • 8 weeks total rollout vs 12+ weeks for simultaneous launch

Key Takeaways

  1. Feature flags enable phased rollouts - Launch features app-by-app instead of all-at-once
  2. Per-app configuration reduces risk - Bugs affect only enabled apps
  3. Legal compliance requires flexibility - Different apps have different regulatory requirements
  4. A/B testing informs strategy - Real data justified social auth investment
  5. Mobile apps need feature discovery - Provide API endpoints for runtime feature detection

Future Enhancements

  1. Database-backed feature flags - Runtime configuration without redeployment
  2. Per-user feature flags - Beta test with specific user cohorts
  3. Percentage rollouts - Enable features for 10%, 50%, then 100% of users
  4. Automatic rollback - Disable features automatically on high error rates

Implementation date: January-February 2026 Commits: a1dcd4f, 4d5a552 Impact: Enabled safe, phased social authentication rollout across 3 apps