Mobile Auth (Better Auth + Expo)

The mobile app uses Better Auth with @better-auth/expo plugin.

The Problem

Better Auth's session state doesn't sync reliably with React context on Expo. The plugin stores cookies in expo-secure-store, but reactive session updates don't propagate as expected.

Our Solution

Custom SessionProvider that:

1. •Initializes from cache - Read cached session from SecureStore on app start
2. •Subscribes to auth signals - Listen to $sessionSignal for auth state changes
3. •Manual refresh - Call onAuthSuccess() after sign-in/sign-up

Reading Cached Session

// src/lib/auth.ts
export function getCachedSession(): AuthSession | null {
  const raw = SecureStore.getItem(SESSION_DATA_KEY);
  // validate and return
}

Session Provider

// src/providers/session-provider.tsx
useEffect(() => {
  const store = getAuthClient().$store;
  const sessionSignal = store.atoms.$sessionSignal;
  const unsubscribe = sessionSignal.subscribe(() => {
    setData(getCachedSession());
  });
  return () => unsubscribe();
}, []);

Required Configuration

Key Files

• •Mobile auth client: apps/frontend/mobile/src/lib/auth.ts
• •Session provider: apps/frontend/mobile/src/providers/session-provider.tsx
• •Backend auth config: apps/backend/api/src/auth.ts

Known Issues

• •Session expiry detection relies on parsing expiresAt from cached data
• •$sessionSignal subscription is undocumented API and may change
• •Web platform falls back to standard cookie-based auth (no SecureStore)

Troubleshooting