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+# Phase 1: Authentication & Account Basics - Research
+
+**Researched:** 2026-01-28
+**Domain:** Flutter + Supabase Authentication
+**Confidence:** HIGH
+
+## Summary
+
+Sage requires Flutter-based authentication using Supabase as the backend service. The established pattern is to use the `supabase_flutter` package (v2.12.0) which provides comprehensive authentication capabilities including email/password signup, password reset, session persistence, and auth state management. The package handles session persistence using SharedPreferences by default, with optional secure storage support via FlutterSecureStorage for enhanced security.
+
+**Primary recommendation:** Use supabase_flutter v2.12.0 with default SharedPreferences storage and PKCE flow for secure authentication across Android and web platforms.
+
+## Standard Stack
+
+The established libraries/tools for this domain:
+
+### Core
+| Library | Version | Purpose | Why Standard |
+|---------|---------|---------|--------------|
+| supabase_flutter | ^2.12.0 | Official Supabase client for Flutter | Provides complete auth implementation, session management, and real-time auth state updates |
+| flutter_secure_storage | ^9.0.0 | Enhanced session security (optional) | Industry standard for storing sensitive data securely on mobile devices |
+| shared_preferences | ^2.0.0 | Default session persistence | Built-in Supabase storage method, lightweight and reliable |
+
+### Supporting
+| Library | Version | Purpose | When to Use |
+|---------|---------|---------|-------------|
+| go_router | ^13.0.0 | Navigation management | For handling auth-based routing and redirects |
+| riverpod | ^2.5.0 | State management | For managing global auth state across the app |
+
+### Alternatives Considered
+| Instead of | Could Use | Tradeoff |
+|------------|-----------|----------|
+| supabase_flutter | firebase_auth | Firebase would work but Supabase is already decided as project standard, better PostgreSQL integration |
+| supabase_flutter | custom auth implementation | Custom auth is significantly more complex, security risks, requires implementing session management, password hashing, token refresh manually |
+
+**Installation:**
+```bash
+flutter pub add supabase_flutter flutter_secure_storage
+```
+
+## Architecture Patterns
+
+### Recommended Project Structure
+```
+src/
+├── lib/
+│   ├── main.dart              # Supabase initialization
+│   ├── core/
+│   │   ├── constants/
+│   │   │   └── supabase_constants.dart    # Supabase URL and keys
+│   │   └── errors/
+│   │       └── auth_exceptions.dart      # Custom auth error handling
+│   ├── features/
+│   │   └── authentication/
+│   │       ├── data/
+│   │       │   └── models/
+│   │       │       └── auth_user.dart      # User model
+│   │       ├── domain/
+│   │       │   └── repositories/
+│   │       │       └── auth_repository.dart   # Auth interface
+│   │       └── presentation/
+│   │           ├── pages/
+│   │           │   ├── login_page.dart
+│   │           │   ├── signup_page.dart
+│   │           │   └── reset_password_page.dart
+│   │           └── widgets/
+│   │               ├── auth_form.dart
+│   │               └── auth_button.dart
+│   └── providers/
+│       └── auth_provider.dart    # Global auth state management
+```
+
+### Pattern 1: Supabase Initialization
+**What:** Initialize Supabase at app startup with proper configuration
+**When to use:** In main.dart before runApp()
+**Example:**
+```dart
+// Source: https://pub.dev/packages/supabase_flutter
+void main() async {
+  WidgetsFlutterBinding.ensureInitialized();
+
+  await Supabase.initialize(
+    url: SUPABASE_URL,
+    anonKey: SUPABASE_ANON_KEY,
+    authOptions: FlutterAuthClientOptions(
+      localStorage: const SharedPreferencesLocalStorage(), // Default, secure enough
+      // For enhanced security on mobile:
+      // localStorage: MySecureStorage(),
+    ),
+  );
+
+  runApp(MyApp());
+}
+
+final supabase = Supabase.instance.client;
+```
+
+### Pattern 2: Auth State Management
+**What:** Use StreamBuilder or Riverpod to listen to auth state changes
+**When to use:** Throughout the app for UI updates based on auth state
+**Example:**
+```dart
+// Source: https://supabase.com/docs/reference/dart/auth-onauthstatechange
+class AuthProvider extends ChangeNotifier {
+  User? _user;
+  User? get user => _user;
+
+  AuthProvider() {
+    supabase.auth.onAuthStateChange.listen((data) {
+      final AuthChangeEvent event = data.event;
+      final Session? session = data.session;
+      
+      _user = session?.user;
+      notifyListeners();
+    });
+  }
+}
+```
+
+### Pattern 3: Authentication Methods
+**What:** Use Supabase auth methods for signup, login, password reset
+**When to use:** For all auth operations
+**Example:**
+```dart
+// Email signup
+final AuthResponse res = await supabase.auth.signUp(
+  email: email,
+  password: password,
+);
+
+// Email login
+final AuthResponse res = await supabase.auth.signInWithPassword(
+  email: email,
+  password: password,
+);
+
+// Password reset
+await supabase.auth.resetPasswordForEmail(
+  email,
+  redirectTo: 'http://example.com/account/update-password',
+);
+```
+
+### Anti-Patterns to Avoid
+- **Manual token management:** Don't store JWT tokens manually or implement custom refresh logic
+- **Ignoring auth state:** Don't skip onAuthStateChange listener - leads to UI inconsistencies
+- **Hardcoded credentials:** Never store Supabase keys directly in code - use environment variables
+
+## Don't Hand-Roll
+
+Problems that look simple but have existing solutions:
+
+| Problem | Don't Build | Use Instead | Why |
+|---------|-------------|-------------|-----|
+| Session persistence | Custom token storage with SharedPreferences | Supabase built-in session management | Handles token expiration, refresh, security automatically |
+| Password reset email flow | Custom SMTP + email templates | Supabase resetPasswordForEmail() | Built-in rate limiting, secure token generation, proper email handling |
+| Auth state management | Manual user state with setState() | onAuthStateChange stream | Automatic updates across all app components |
+| Error handling | Try-catch for every auth call | AuthException handling | Consistent error messages, proper user feedback |
+
+**Key insight:** Supabase handles all security-critical aspects like token refresh, session validation, and password reset flow securely. Custom implementations risk security vulnerabilities.
+
+## Common Pitfalls
+
+### Pitfall 1: Session Not Persisting
+**What goes wrong:** User gets logged out when app restarts
+**Why it happens:** Missing localStorage configuration or using EmptyLocalStorage
+**How to avoid:** Ensure proper initialization with default localStorage
+**Warning signs:** User must log in every time app launches
+
+### Pitfall 2: Auth State Not Updating UI
+**What goes wrong:** UI doesn't reflect login/logout status
+**Why it happens:** Not listening to onAuthStateChange events
+**How to avoid:** Always subscribe to auth state changes in app initialization
+**Warning signs:** User stuck on login screen after successful authentication
+
+### Pitfall 3: Password Reset Flow Fails
+**What goes wrong:** Reset links don't work or redirect incorrectly
+**Why it happens:** Missing redirect URL configuration in Supabase dashboard
+**How to avoid:** Configure redirect URLs in Authentication > URL Configuration
+**Warning signs:** Users report broken password reset emails
+
+### Pitfall 4: Web Service Worker Issues
+**What goes wrong:** Flutter web app fails to register service worker
+**Why it happens:** Improper web hosting configuration for password reset callback
+**How to avoid:** Ensure web server serves correct MIME types for service workers
+**Warning signs:** Console errors about service worker MIME types
+
+### Pitfall 5: Environment Variable Exposure
+**What goes wrong:** Supabase keys exposed in client code
+**Why it happens:** Hardcoding values instead of using environment variables
+**How to avoid:** Use flutter_dotenv for local dev, proper CI/CD secrets for production
+**Warning signs:** Keys visible in compiled code or version control
+
+## Code Examples
+
+Verified patterns from official sources:
+
+### Email Sign Up
+```dart
+// Source: https://supabase.com/docs/reference/dart/auth-signup
+final AuthResponse res = await supabase.auth.signUp(
+  email: 'example@email.com',
+  password: 'example-password',
+);
+final Session? session = res.session;
+final User? user = res.user;
+```
+
+### Email Sign In
+```dart
+// Source: https://supabase.com/docs/reference/dart/auth-signinwithpassword
+final AuthResponse res = await supabase.auth.signInWithPassword(
+  email: 'example@email.com',
+  password: 'example-password',
+);
+final Session? session = res.session;
+final User? user = res.user;
+```
+
+### Password Reset
+```dart
+// Source: https://supabase.com/docs/guides/auth/passwords
+await supabase.auth.resetPasswordForEmail(
+  'valid.email@supabase.io', 
+  redirectTo: 'http://example.com/account/update-password',
+);
+```
+
+### Auth State Listening
+```dart
+// Source: https://supabase.com/docs/reference/dart/auth-onauthstatechange
+final authSubscription = supabase.auth.onAuthStateChange.listen((data) {
+  final AuthChangeEvent event = data.event;
+  final Session? session = data.session;
+  
+  switch (event) {
+    case AuthChangeEvent.signedIn:
+      // Navigate to home
+      break;
+    case AuthChangeEvent.signedOut:
+      // Navigate to login
+      break;
+  }
+});
+```
+
+### Secure Storage Option
+```dart
+// Source: https://pub.dev/packages/supabase_flutter
+class MySecureStorage extends LocalStorage {
+  final storage = FlutterSecureStorage();
+
+  @override
+  Future<void> initialize() async {}
+
+  @override
+  Future<String?> accessToken() async {
+    return storage.read(key: supabasePersistSessionKey);
+  }
+
+  @override
+  Future<void> persistSession(String persistSessionString) async {
+    return storage.write(key: supabasePersistSessionKey, value: persistSessionString);
+  }
+
+  @override
+  Future<void> removePersistedSession() async {
+    return storage.delete(key: supabasePersistSessionKey);
+  }
+}
+```
+
+## State of the Art
+
+| Old Approach | Current Approach | When Changed | Impact |
+|--------------|-----------------|--------------|--------|
+| Hive-based storage (v1) | SharedPreferences-based storage (v2) | v2.0 release | Simpler, faster app startup, better platform support |
+| Implicit auth flow | PKCE flow (default in v2) | v2.0 release | More secure for deep links and OAuth |
+| Manual token refresh | Automatic token refresh | v1.x | Session persistence handled automatically |
+| SupabaseAuth class | Direct client access | v2.0 release | Cleaner API, no wrapper classes needed |
+
+**Deprecated/outdated:**
+- **SupabaseAuth.initialSession**: Use supabase.auth.currentSession instead
+- **Hive storage**: Replaced with SharedPreferences in v2
+- **signInWithApple() method**: Removed from core package, use separate sign_in_with_apple package
+- **Provider enum**: Renamed to OAuthProvider to avoid conflicts
+
+## Open Questions
+
+1. **Enhanced Security Requirements**
+   - What we know: FlutterSecureStorage available for enhanced session security
+   - What's unclear: Does Sage require enhanced security for food inventory app sensitivity?
+   - Recommendation: Use SharedPreferences for v1, evaluate FlutterSecureStorage for production
+
+2. **Email Template Customization**
+   - What we know: Supabase provides default email templates
+   - What's unclear: Does Sage need custom branding for password reset emails?
+   - Recommendation: Use default templates for v1, customize after user feedback
+
+3. **Rate Limiting Strategy**
+   - What we know: Supabase has built-in rate limiting (2 emails/hour default)
+   - What's unclear: Are these limits sufficient for household app usage patterns?
+   - Recommendation: Monitor and configure custom SMTP if limits are reached
+
+## Sources
+
+### Primary (HIGH confidence)
+- supabase_flutter v2.12.0 documentation - Authentication methods, session management, initialization patterns
+- Supabase official docs - Password reset flow, email authentication best practices
+
+### Secondary (MEDIUM confidence)
+- Flutter Secure Storage package documentation - Enhanced session persistence options
+- Medium articles on Flutter auth patterns - Real-world implementation patterns (verified with official docs)
+
+### Tertiary (LOW confidence)
+- Stack Overflow discussions on specific error scenarios - Limited verification, use with caution
+
+## Metadata
+
+**Confidence breakdown:**
+- Standard stack: HIGH - Based on official Supabase Flutter package documentation
+- Architecture: HIGH - Verified with multiple official sources and community patterns
+- Pitfalls: HIGH - Official documentation clearly documents common issues and solutions
+
+**Research date:** 2026-01-28
+**Valid until:** 2026-02-27 (30 days for stable authentication libraries)
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