feat(ios): implement authentication and Keychain sessions

[Tutitoos]

Plan reference

Post-1.0 — iPhone and iPad: secure native identity.

Objective

Implement server discovery, bootstrap when permitted, email and password, passkeys, recovery code, short JWT refresh, per-device revocation, Keychain storage, logout, and protected-screen behavior.

Scope

• Add AuthenticationServices flows, native token exchange, Keychain access control, installation identity, refresh coordination actor, biometric policy where appropriate, recovery, revocation, and secure logout.

Tasks

• Define Swift 6 models, actors, storage, API, and UI boundaries for this scope.
• Implement the smallest complete native capability.
• Add XCTest, Swift Concurrency, migration, UI, accessibility, and device tests where applicable.
• Update generated clients, translations, privacy declarations, and distribution documentation.

Acceptance criteria

• Refresh credentials never enter GRDB, preferences, logs, URLs, crash events, or backups outside Keychain policy.

• Concurrent requests perform one refresh and correctly replay authorized operations.

• Revoked devices cannot refresh and return to a safe sign-in state.

• Logout clears credentials, cached mail, notifications, and background work.

• Account isolation, data protection, accessibility, EN default, and ES completeness match the web and macOS contracts.

• Tokens, credentials, message content, recipients, and personal data never enter logs, crash reports, screenshots, fixtures, URLs, or notification defaults.

• The capability is independently reviewable and rollback-safe.

Validation

• Run passkey, password, recovery, refresh race, locked device, Keychain failure, revocation, logout, reinstall, and physical-device tests.

• Run Swift build, XCTest, strict concurrency checks, generated-client diff, and the affected simulator and physical-device UI tests.

• Use sanitized fixtures and protected accounts only for final manual provider validation.

Dependencies

Post-1.0 work. Blocked until Mailflow 1.0.0 is released: https://github.com/Tutitoos/mailflow/milestone/9

Risks

Offline state, background execution, notification privacy, generated contracts, and device credentials can diverge from server truth. Use actors, Keychain, bounded caches, explicit conflict states, and real-device validation.

Out of scope

• Social sign-in, multi-user instances, enterprise SSO, and credential synchronization between devices.