code: public Observable<RegistryListCredentialsResultInner> listCredentialsAsync(String resourceGroupName, String registryName) {
          return listCredentialsWithServiceResponseAsync(resourceGroupName, registryName).map(new Func1<ServiceResponse<RegistryListCredentialsResultInner>, RegistryListCredentialsResultInner>() {
              @Override
              public RegistryListCredentialsResultInner call(ServiceResponse<RegistryListCredentialsResultInner> response) {
                  return response.body();
              }
          });
      }
docs: Lists the login credentials for the specified container registry.
  
  @param resourceGroupName The name of the resource group to which the container registry belongs.
  @param registryName The name of the container registry.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the RegistryListCredentialsResultInner object