davidortinau/maui-skills/maui-secure-storage

Secure Storage — Gotchas & Best Practices

Critical Platform Pitfalls

⚠️ Android: Auto Backup Breaks Encrypted Values

Auto Backup restores encrypted preferences to a new device where the encryption key is invalid — this throws unrecoverable exceptions. You must either disable Auto Backup or exclude secure storage files from backup. See references/secure-storage-api.md for setup options.

⚠️ Android: Always Wrap in try/catch

Corrupted values from backup restoration throw exceptions. Never call GetAsync unprotected:

// ❌ Unprotected — crashes on corrupted backup data
var value = await SecureStorage.Default.GetAsync("key");
 
// ✅ Protected — handles corruption gracefully
try
{
    var value = await SecureStorage.Default.GetAsync("key");
}
catch (Exception)
{
    SecureStorage.Default.RemoveAll();
}

⚠️ iOS: Keychain Entitlements on Simulator

Add keychain access groups for Simulator builds, but remove before physical device / App Store builds — they cause signing issues on devices where they aren't needed.

⚠️ iOS: Uninstall Does NOT Clear Keychain

Unlike Android, uninstalling an iOS app does not remove its Keychain entries. Values persist and are available if the app is reinstalled. Design for this — don't assume a fresh install means empty storage.

⚠️ iOS: iCloud Keychain Sync

Values may sync across devices via iCloud Keychain if the user has it enabled. This is platform behavior, not controllable from MAUI. Don't store device-specific tokens that shouldn't roam.

Windows Limits

• Key name: max 255 characters
• Value: max 8 KB per setting
• Composite storage: max 64 KB total

Common Mistakes

// ❌ Storing large data — SecureStorage is for small secrets only
await SecureStorage.Default.SetAsync("profile_image", base64EncodedImage);
 
// ✅ Store tokens, passwords, short secrets
await SecureStorage.Default.SetAsync("auth_token", jwtToken);
 
// ❌ Logging secret values
_logger.LogInformation("Token: {Token}", await SecureStorage.Default.GetAsync("auth_token"));
 
// ✅ Log existence, not value
_logger.LogInformation("Token exists: {Exists}", token is not null);
 
// ❌ Storing complex objects without serialization (values are strings only)
await SecureStorage.Default.SetAsync("user", userObject);
 
// ✅ Serialize to JSON first
await SecureStorage.Default.SetAsync("user", JsonSerializer.Serialize(user));

Decision Framework

Testability: Always Use DI

Never call SecureStorage.Default directly from ViewModels — wrap it in an ISecureStorageService interface for testability. See references/secure-storage-api.md for the full DI wrapper pattern with mock examples.

// ❌ Direct static access — untestable
public class LoginViewModel
{
    public async Task SaveToken(string token)
        => await SecureStorage.Default.SetAsync("auth_token", token);
}
 
// ✅ Inject interface — testable and mockable
public class LoginViewModel(ISecureStorageService secure)
{
    public async Task SaveToken(string token)
        => await secure.SetAsync("auth_token", token);
}

Checklist

• [ ] Android: Auto Backup disabled or secure storage excluded from backup
• [ ] Android: All GetAsync calls wrapped in try/catch
• [ ] iOS: Keychain entitlements configured (Simulator only — remove for device builds)
• [ ] Values are strings only — complex data serialized to JSON
• [ ] No secret values logged anywhere
• [ ] SecureStorage.Default accessed via DI wrapper, not directly from ViewModels