code: @SuppressWarnings("WeakerAccess")
      private ParameterizableRequest<Void, AuthenticationException> passwordless() {
          HttpUrl url = HttpUrl.parse(auth0.getDomainUrl()).newBuilder()
                  .addPathSegment(PASSWORDLESS_PATH)
                  .addPathSegment(START_PATH)
                  .build();
  
          final Map<String, Object> parameters = ParameterBuilder.newBuilder()
                  .setClientId(getClientId())
                  .asDictionary();
  
          return factory.POST(url, client, gson, authErrorBuilder)
                  .addParameters(parameters);
      }
docs: Start a custom passwordless flow
  
  @return a request to configure and start