code: public Observable<ServiceResponse<CertificateWithNonceDescriptionInner>> generateVerificationCodeWithServiceResponseAsync(String resourceGroupName, String resourceName, String certificateName, String ifMatch) {
          if (this.client.subscriptionId() == null) {
              throw new IllegalArgumentException("Parameter this.client.subscriptionId() is required and cannot be null.");
          }
          if (resourceGroupName == null) {
              throw new IllegalArgumentException("Parameter resourceGroupName is required and cannot be null.");
          }
          if (resourceName == null) {
              throw new IllegalArgumentException("Parameter resourceName is required and cannot be null.");
          }
          if (certificateName == null) {
              throw new IllegalArgumentException("Parameter certificateName is required and cannot be null.");
          }
          if (this.client.apiVersion() == null) {
              throw new IllegalArgumentException("Parameter this.client.apiVersion() is required and cannot be null.");
          }
          if (ifMatch == null) {
              throw new IllegalArgumentException("Parameter ifMatch is required and cannot be null.");
          }
          return service.generateVerificationCode(this.client.subscriptionId(), resourceGroupName, resourceName, certificateName, this.client.apiVersion(), ifMatch, this.client.acceptLanguage(), this.client.userAgent())
              .flatMap(new Func1<Response<ResponseBody>, Observable<ServiceResponse<CertificateWithNonceDescriptionInner>>>() {
                  @Override
                  public Observable<ServiceResponse<CertificateWithNonceDescriptionInner>> call(Response<ResponseBody> response) {
                      try {
                          ServiceResponse<CertificateWithNonceDescriptionInner> clientResponse = generateVerificationCodeDelegate(response);
                          return Observable.just(clientResponse);
                      } catch (Throwable t) {
                          return Observable.error(t);
                      }
                  }
              });
      }
docs: Generate verification code for proof of possession flow.
  Generates verification code for proof of possession flow. The verification code will be used to generate a leaf 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
  @param ifMatch ETag of the Certificate.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the observable to the CertificateWithNonceDescriptionInner object