code: static String getAccessTokenForUserId(String userId) {
          if (userId == null && getUserId() == null
                  || userId != null && userId.equals(getUserId())) {
              return getAccessToken();
          } else {
              JSONObject usersArchive = getJSONObject(PER_USER_ARCHIVE_PREF_NAME);
              if (usersArchive == null) usersArchive = new JSONObject();
              JSONObject userArchive = usersArchive.optJSONObject(userId == null ? "" : userId);
              if (userArchive == null) userArchive = new JSONObject();
              return JSONUtil.optString(userArchive, ACCESS_TOKEN_PREF_NAME);
          }
      }
docs: Get the access token associated to a given user's shared preferences.