Firebase

Future<void> signInWithCustomToken(String customToken) async {
  try {
    UserCredential userCredential = await FirebaseAuth.instance.signInWithCustomToken(customToken);
    print('Successfully signed in with custom token: ${userCredential.user.uid}');
  } catch (e) {
    print('Error signing in with custom token: $e');
  }
}

// 例として、サーバーサイドから取得したカスタムトークンを使用
String customToken = 'your-custom-token-from-server';
signInWithCustomToken(customToken);