Need to add email/password authentication alongside existing OAuth flows (Spotify, Google, Apple Music) in a Next.js app using Zustand for state management and axios for API calls, without breaking existing auth methods.

When integrating Apple Music via MusicKit JS, the music_user_token returned by authorize() is NOT stable across sessions. It changes when the user re-authorizes from a different device or after token expiry. Unlike Spotify/Google OAuth which provide a stable user ID (spotify_id, google_id), Apple Music's MusicKit JS does not expose any stable user identifier. Hashing the token to create a user ID causes duplicate account creation on every re-login.