docs: public String rtmpPublishUrl(String streamKey, int expireAfterSeconds) {
          long expire = System.currentTimeMillis() / 1000 + expireAfterSeconds;
          String path = String.format("/%s/%s?e=%d", hub, streamKey, expire);
          String token;
          try {
              token = auth.sign(path);
          } catch (Exception e) {
              e.printStackTrace();
              return null;
          }
          return String.format("rtmp://%s%s&token=%s", rtmpPublishDomain, path, token);
      }