signOutAll method
모든 Provider 로그아웃
Implementation
Future<List<AuthResult>> signOutAll() async {
if (delay != null) {
await Future.delayed(delay!);
}
_currentUser = null;
_serverToken = null;
_expiresAt = null;
_authStateController.add(null);
return configuredProviders
.map((p) => AuthResult.success(provider: p, user: null))
.toList();
}