FirebaseAuthBackend

Firebase implementation of AuthProviderBackend, KMPAuth's default backend. Registered automatically the first time a Firebase container is used; register a different backend at application start to override.

Token-based credentials (AuthCredential.IdToken from Google or Facebook) are exchanged directly. Apple and web-flow sign-in (AuthCredential.OAuthWebFlow) require a platform-driven browser flow and are served by the dedicated composables (AppleButtonUiContainer, GithubButtonUiContainer, OAuthContainer) rather than this backend.