code: @VisibleForTesting
    void setAuthenticationHeaders(Object soapClient, Map<String, Object> headerElements,
        AdWordsSession adWordsSession) throws AuthenticationException {
      authorizationHeaderHandler.setAuthorization(soapClient, adWordsSession);
    }
docs: Sets the authentication headers.
  
  @param soapClient the SOAP client
  @param headerElements the map housing header elements
  @param adWordsSession the AdWords session
  @throws AuthenticationException if there was a problem getting/setting the
  header