+ /**
+ * Calls the API to get an access token
+ *
+ * @function getAccessToken
+ * @memberof TwitterHelper
+ * @instance
+ * @param {string} oAuthToken An oAuth request token
+ * @param {string} oAuthVerifier An oAuth verifier sent from the
+ * twitter callback
+ * @return {Promise<TwitterHelper.tAccessToken>} the acess token response
+ */