onboard method
Returns true
if authentication is successful for the existing atsign in device.
Implementation
Future<bool> onboard() async {
AtClientService atClientServiceInstance =
_getClientServiceForAtsign(_atsign)!;
bool result = await atClientServiceInstance.onboard(
atClientPreference: _atClientPreference, atsign: _atsign);
_atsign ??= await getAtSign();
atClientServiceMap.putIfAbsent(_atsign, () => atClientServiceInstance);
await _sync(_atsign);
return result;
}