code: public ServiceFuture<P2SVpnServerConfigurationInner> createOrUpdateAsync(String resourceGroupName, String virtualWanName, String p2SVpnServerConfigurationName, P2SVpnServerConfigurationInner p2SVpnServerConfigurationParameters, final ServiceCallback<P2SVpnServerConfigurationInner> serviceCallback) {
          return ServiceFuture.fromResponse(createOrUpdateWithServiceResponseAsync(resourceGroupName, virtualWanName, p2SVpnServerConfigurationName, p2SVpnServerConfigurationParameters), serviceCallback);
      }
docs: Creates a P2SVpnServerConfiguration to associate with a VirtualWan if it doesn't exist else updates the existing P2SVpnServerConfiguration.
  
  @param resourceGroupName The resource group name of the VirtualWan.
  @param virtualWanName The name of the VirtualWan.
  @param p2SVpnServerConfigurationName The name of the P2SVpnServerConfiguration.
  @param p2SVpnServerConfigurationParameters Parameters supplied to create or Update a P2SVpnServerConfiguration.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object