code: public Observable<Void> beginDownloadAsync(String resourceGroupName, String virtualWANName, GetVpnSitesConfigurationRequest request) {
          return beginDownloadWithServiceResponseAsync(resourceGroupName, virtualWANName, request).map(new Func1<ServiceResponse<Void>, Void>() {
              @Override
              public Void call(ServiceResponse<Void> response) {
                  return response.body();
              }
          });
      }
docs: Gives the sas-url to download the configurations for vpn-sites in a resource group.
  
  @param resourceGroupName The resource group name.
  @param virtualWANName The name of the VirtualWAN for which configuration of all vpn-sites is needed.
  @param request Parameters supplied to download vpn-sites configuration.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceResponse} object if successful.