code: public RequestToken retrieveAccessToken(RequestToken token, String verifier) {
          OAuthConsumer consumer = new DefaultOAuthConsumer(info.key.key, info.key.secret);
          consumer.setTokenWithSecret(token.token, token.secret);
          try {
              provider.retrieveAccessToken(consumer, verifier);
              return new RequestToken(consumer.getToken(), consumer.getTokenSecret());
          } catch (OAuthException ex) {
              throw new RuntimeException(ex);
          }
      }
docs: Exchange a request token for an access token.
  
  @param token    the token/secret pair obtained from a previous call
  @param verifier a string you got through your user, with redirection
  @return A Right(RequestToken) in case of success, Left(OAuthException) otherwise