code: private String buildOAuth1Url(OAuth1ConnectionFactory<?> connectionFactory, NativeWebRequest request, MultiValueMap<String, String> additionalParameters) {
  		OAuth1Operations oauthOperations = connectionFactory.getOAuthOperations();
  		MultiValueMap<String, String> requestParameters = getRequestParameters(request);
  		OAuth1Parameters parameters = getOAuth1Parameters(request, additionalParameters);
  		parameters.putAll(requestParameters);
  		if (oauthOperations.getVersion() == OAuth1Version.CORE_10) {
  			parameters.setCallbackUrl(callbackUrl(request));
  		}
  		OAuthToken requestToken = fetchRequestToken(request, requestParameters, oauthOperations);
  		sessionStrategy.setAttribute(request, OAUTH_TOKEN_ATTRIBUTE, requestToken);
  		return buildOAuth1Url(oauthOperations, requestToken.getValue(), parameters);
  	}
docs: internal helpers