Apple's message
Moreover, we found that your app uses Sina and Tencent Weibo login for authentication purposes only - but does not include any account-based features offered by that site. This is not in compliance with the App Store Review Guidelines.It would be appropriate to modify your app to include account-based features of that social network - or use your own authentication mechanism.
I don't know what is meant by "include account-based features of that social network". How can I fix this?
Sina and Tencent Weibo is the same as Facebook or Twitter.
You need some additional features like sharing content with friends or similar which actually provides a reason for you to require the user to login. If you already have that feature, reply to the rejection with details about where in the app that function is.