code: public Observable<CertificateDescriptionInner> getAsync(String resourceGroupName, String resourceName, String certificateName) {
          return getWithServiceResponseAsync(resourceGroupName, resourceName, certificateName).map(new Func1<ServiceResponse<CertificateDescriptionInner>, CertificateDescriptionInner>() {
              @Override
              public CertificateDescriptionInner call(ServiceResponse<CertificateDescriptionInner> response) {
                  return response.body();
              }
          });
      }
docs: Get the certificate.
  Returns the certificate.
  
  @param resourceGroupName The name of the resource group that contains the IoT hub.
  @param resourceName The name of the IoT hub.
  @param certificateName The name of the certificate
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the CertificateDescriptionInner object