docs: protected Future<OAuth2AccessToken> sendAccessTokenRequestAsync(OAuthRequest request,
              OAuthAsyncRequestCallback<OAuth2AccessToken> callback) {
  
          return execute(request, callback, new OAuthRequest.ResponseConverter<OAuth2AccessToken>() {
              @Override
              public OAuth2AccessToken convert(Response response) throws IOException {
                  return getApi().getAccessTokenExtractor().extract(response);
              }
          });
      }