code: public Observable<ServiceResponse<BackupCertificateResult>> backupCertificateWithServiceResponseAsync(String vaultBaseUrl, String certificateName) {
          if (vaultBaseUrl == null) {
              throw new IllegalArgumentException("Parameter vaultBaseUrl is required and cannot be null.");
          }
          if (certificateName == null) {
              throw new IllegalArgumentException("Parameter certificateName is required and cannot be null.");
          }
          if (this.apiVersion() == null) {
              throw new IllegalArgumentException("Parameter this.apiVersion() is required and cannot be null.");
          }
          String parameterizedHost = Joiner.on(", ").join("{vaultBaseUrl}", vaultBaseUrl);
          return service.backupCertificate(certificateName, this.apiVersion(), this.acceptLanguage(), parameterizedHost, this.userAgent())
              .flatMap(new Func1<Response<ResponseBody>, Observable<ServiceResponse<BackupCertificateResult>>>() {
                  @Override
                  public Observable<ServiceResponse<BackupCertificateResult>> call(Response<ResponseBody> response) {
                      try {
                          ServiceResponse<BackupCertificateResult> clientResponse = backupCertificateDelegate(response);
                          return Observable.just(clientResponse);
                      } catch (Throwable t) {
                          return Observable.error(t);
                      }
                  }
              });
      }
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
  @return the observable to the BackupCertificateResult object