saveInstallationId method
Keeps the installation your backend answered for this key, which may not be the ID proposed. Only this opaque ID is stored here; the private key never leaves the platform's keystore.
Implementation
Future<void> saveInstallationId(String installationId) {
return _storage.write(
key: _installationIdKey,
value: installationId,
iOptions: _iosOptions,
);
}