Implement step-up auth for sensitive screens
epic-biometric-session-authentication-core-services-task-009 — Implement the step-up authentication API on BiometricAuthService that allows sensitive screens (such as encrypted contact assignment views for Blindeforbundet) to require fresh biometric verification before displaying protected content. Returns a typed StepUpAuthResult that callers use to gate access, without requiring a full re-login flow.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 6 - 158 tasks
Can start after Tier 5 completes
Implementation Notes
Implement requestStepUpAuth() as a separate method on BiometricAuthService distinct from the session-login authenticate() method — different semantics (presence proof vs. session establishment). Store the step-up grant as a DateTime? _stepUpGrantedAt field on the service instance (null = not granted, non-null = granted at that time).
In each requestStepUpAuth() call, first check if _stepUpGrantedAt is non-null and within the validity window — if so, return StepUpAuthResult.granted immediately. Register a WidgetsBindingObserver on the service to clear _stepUpGrantedAt when AppLifecycleState transitions to paused or inactive. Pass the localizedReason parameter to LocalAuthentication.authenticate() so the iOS/Android native dialog displays the context to the user. For Blindeforbundet's encrypted assignment views, document a clear pattern: decrypt content only after awaiting StepUpAuthResult.granted, and clear the decrypted data from memory when step-up expires.
Testing Requirements
Unit tests: step-up returns granted on biometric success, denied on failure/cancel, unavailable on hardware absence. Test validity window: a second requestStepUpAuth() call within 5 minutes returns granted immediately without re-prompting. Test validity window expiry: a call after window expires re-triggers biometric prompt. Test app-background reset: simulating AppLifecycleState.paused invalidates the step-up grant.
Integration test on device verifying the native dialog shows the reason string. Test that sensitive screen content is not rendered until StepUpAuthResult.granted is received.
Multiple concurrent callers (e.g., SessionResumeManager and a background sync service) could simultaneously detect a near-expired token and each invoke SupabaseSessionManager.refreshSession(), causing duplicate refresh API calls and potentially a token invalidation race condition on the Supabase Auth server. This can result in one caller receiving a valid refreshed token while another receives a 401, causing intermittent authentication failures.
Mitigation & Contingency
Mitigation: Implement a single-flight pattern inside SupabaseSessionManager so that concurrent refresh calls coalesce into one in-flight request. Use a Dart Completer or AsyncMemoizer to ensure all waiters receive the same refreshed token. Write a concurrent integration test to validate the single-flight behaviour.
Contingency: If the single-flight pattern introduces deadlocks or timeout complexity, fall back to a mutex-based lock with a 10-second timeout, logging a warning if the lock is held longer than expected, and triggering a full re-login if the refresh ultimately fails.
Supabase Row-Level Security policies evaluate the JWT claims (user_id, role, org_id) on every query. If the refreshed token contains stale or changed claims — for example if a coordinator's role was updated server-side — RLS may silently block data access even though the session appears valid from the client's perspective, causing confusing empty screens rather than an authentication error.
Mitigation & Contingency
Mitigation: After every token refresh, decode the new JWT and compare key claims (role, org_id) with the cached values. If claims have changed, emit a session-claims-changed event that triggers a role re-resolution and navigation reset. Document this behaviour in the SupabaseSessionManager API contract.
Contingency: If claims drift is detected in production and causes data visibility issues, provide a force-refresh mechanism in the UI (pull-to-refresh on home screen) that clears cached role state and re-fetches from Supabase, accompanied by a user-visible toast indicating the session was refreshed.
Allowing session resumption from cached local token when offline introduces a window where a revoked or invalidated session can still grant app access. For example, if a coordinator deactivates a peer mentor's account while the mentor is offline, the mentor continues to have access until connectivity is restored and the token is validated server-side.
Mitigation & Contingency
Mitigation: Set a maximum offline grace period (e.g., 24 hours) stored alongside the token in SecureSessionStorage. If the grace period is exceeded, force a full credential re-login regardless of connectivity status. Scope offline access to read-only operations only, requiring connectivity for any write that reaches Supabase.
Contingency: If the offline grace period logic is found to be insufficient for compliance, implement remote session invalidation via a lightweight push notification that clears SecureSessionStorage even when the app is backgrounded, using FCM with a data-only message.