Implement BankID assertion validation via Edge Function
epic-bankid-vipps-login-services-task-008 — Implement the BankID assertion validation step in the BankID Authentication Service: poll or receive callback for the completed BankID assertion, call the Supabase Edge Function that performs server-side BankID certificate validation, handle polling timeout and user cancellation, and parse the validated identity response including the verified national identity.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 4 - 323 tasks
Can start after Tier 3 completes
Implementation Notes
Implement polling as a Dart Timer.periodic(Duration(seconds: 2), ...) that calls the Edge Function and processes the response. Wrap the poll counter in a final counter variable; cancel the timer when counter >= 90 or when a terminal state (complete/failed/cancelled) is received. Use WidgetsBindingObserver to implement AppLifecycleState monitoring — pause the timer on paused and restart on resumed. The Edge Function POST /bankid-collect should call the BankID /collect endpoint with the orderRef, validate the certificate chain, extract the personnummer from the completionData.user.personalNumber field, and return only the extracted identity fields (no raw BankID objects).
After receiving 'complete', immediately cancel the polling timer, clear sessionId from flutter_secure_storage, and pass the identity to the same Supabase user persistence logic used by Vipps (task-006). Reuse the consent dialog for NIN storage consent — the UX should be consistent between Vipps and BankID login paths. Handle BankID-specific error codes: 'expiredTransaction', 'certificateErr', 'userCancel', 'cancelled', 'startFailed' each mapped to appropriate AuthState.error sub-types.
Testing Requirements
Unit tests (flutter_test): mock Timer.periodic and Edge Function responses to test the full polling state machine. Verify polling stops at 90 attempts and emits AuthState.error. Verify 'cancelled' response emits AuthState.unauthenticated. Verify 'complete' response triggers the downstream persistence layer (mock).
Verify polling suspends on AppLifecycleState.paused and resumes on AppLifecycleState.resumed. Verify early termination when deep link callback received. Integration tests: run against BankID sandbox environment, simulate user completing authentication in BankID test app, verify end-to-end flow completes. Security tests: attempt to poll with a mismatched sessionId, verify Edge Function rejects it.
Verify no BankID certificate material is present in the Flutter response objects. Target 95%+ branch coverage on the polling state machine.
The PKCE OAuth flow requires the code verifier to survive an app backgrounding during the Vipps redirect, which can trigger OS memory pressure and clear in-memory state. If the verifier is lost between authorization request and callback, the token exchange fails and the user is stranded with a confusing error.
Mitigation & Contingency
Mitigation: Store the PKCE code verifier in AuthTokenStore (Flutter Secure Storage) immediately after generation, before launching the Vipps redirect. Clear it only after a successful or explicitly failed token exchange.
Contingency: If state loss occurs in production, implement a retry flow that generates a new PKCE pair and restarts the authorization URL request, with a user-visible 'Try again' prompt rather than a generic error.
Resuming a Supabase session after biometric verification requires the session token to still be valid. If the session has expired in the background (e.g., after a long device offline period), biometric success will not produce a valid session, and the user will see a confusing 'Face ID worked but still logged out' experience.
Mitigation & Contingency
Mitigation: Before presenting the biometric prompt, check session token expiry. If expired, skip biometrics and route directly to full BankID/Vipps re-authentication. Only offer biometric re-auth if the stored refresh token is still within its validity window.
Contingency: If session expiry during biometric flow occurs in production, implement a graceful transition message ('Your session has expired — please log in again') that preserves the user's last-used authentication method preference.
BankID and Vipps may return different user identifiers (personnummer, phone number, sub claim) that must be correctly linked to an existing Supabase auth user. If the linking logic has edge cases (e.g., user previously registered via email/password), duplicate Supabase accounts may be created.
Mitigation & Contingency
Mitigation: Design the identity linking logic with explicit disambiguation: check for existing users by personnummer before creating a new Supabase identity. Implement the linking via Supabase Edge Function to keep the logic server-side and auditable.
Contingency: Implement an admin-facing account merge tool in the admin portal to resolve duplicate accounts if they occur. Add a Supabase unique constraint on the personnummer field to make duplicates fail loudly rather than silently.
The Vipps nin (personnummer) scope requires explicit approval from Vipps as part of the merchant agreement. If this scope approval is not in place before the production release, the Vipps flow will succeed but return no personnummer, making the primary business value (membership data gap fill) non-functional without user-visible error.
Mitigation & Contingency
Mitigation: Apply for Vipps nin scope approval as part of the merchant onboarding process, well before Phase 2 launch. Implement the service to gracefully handle absent nin claims and show users a clear message if personnummer could not be retrieved.
Contingency: If nin scope is delayed, ship the Vipps login flow without personnummer write-back first (delivering login value immediately) and add personnummer sync as a post-approval update with no UI changes required.