getCachedDeviceKeyAndPassword method 
    
      
Future<void>
getCachedDeviceKeyAndPassword(
)
      
     
    
    
  Implementation
  Future<void> getCachedDeviceKeyAndPassword() async {
  final deviceKeyKey = '$keyPrefix.deviceKey';
  final randomPasswordKey = '$keyPrefix.randomPasswordKey';
  final deviceGroupKeyKey = '$keyPrefix.deviceGroupKey';
  if (await storage.getItem(deviceKeyKey) != null) {
    _deviceKey = await storage.getItem(deviceKeyKey);
    _deviceGroupKey = await storage.getItem(deviceGroupKeyKey);
    _randomPassword = await storage.getItem(randomPasswordKey);
  }
}