code: public Observable<RegistryCredentialsInner> getCredentialsAsync(String resourceGroupName, String registryName) {
          return getCredentialsWithServiceResponseAsync(resourceGroupName, registryName).map(new Func1<ServiceResponse<RegistryCredentialsInner>, RegistryCredentialsInner>() {
              @Override
              public RegistryCredentialsInner call(ServiceResponse<RegistryCredentialsInner> response) {
                  return response.body();
              }
          });
      }
docs: Gets the administrator 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 RegistryCredentialsInner object