1. user guide on google
https://developers.google.com/google-apps/calendar/instantiate
2. google app console for developers
https://developers.google.com/google-apps/calendar/instantiate
3.set up oauth info
notes:you need to set your redirect uris both on google console and in your coode. that is,you need to set up redirect uris on two place.
4. unbind your account, rebind your account, let me get a new refreshtoekn again
https://www.google.com/settings/u/1/security