code: public BackupCertificateResult backupCertificate(String vaultBaseUrl, String certificateName) {
          return backupCertificateWithServiceResponseAsync(vaultBaseUrl, certificateName).toBlocking().single().body();
      }
docs: Backs up the specified certificate.
  Requests that a backup of the specified certificate be downloaded to the client. All versions of the certificate will be downloaded. This operation requires the certificates/backup permission.
  
  @param vaultBaseUrl The vault name, for example https://myvault.vault.azure.net.
  @param certificateName The name of the certificate.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @throws KeyVaultErrorException thrown if the request is rejected by server
  @throws RuntimeException all other wrapped checked exceptions if the request fails to be sent
  @return the BackupCertificateResult object if successful.