*/
public Token getAccessToken(Token requestToken, Verifier verifier) {
OAuthRequest request = new OAuthRequest(api.getAccessTokenVerb(), api.getAccessTokenEndpoint());
request.addQuerystringParameter(OAuthConstants.CLIENT_ID, config.getApiKey());
request.addQuerystringParameter(OAuthConstants.CLIENT_SECRET, config.getApiSecret());
request.addQuerystringParameter(OAuthConstants.CODE, verifier.getValue());
request.addQuerystringParameter(OAuthConstants.REDIRECT_URI, config.getCallback());
request.addQuerystringParameter("grant_type", "authorization_code");
if (config.hasScope()) {
request.addQuerystringParameter(OAuthConstants.SCOPE, config.getScope());