PHP and Google Calendar two way sync

I have a website where users can register and login. Each user has their own custom calendar on my site. I want a feature where they can connect/login with their Google account and my site so that it has two way sync. For example, if the user makes a change in the calendar on my site, it will edit and reflect the changes on the Google Calendar. For example, if bob123 logs in on my website and connects his account to Google Calendar (bob123@[login to view URL]), then it will have two way sync enabled for his account. If another user named john456 logs into my website and connects his Google Calendar account (john456@[login to view URL]), it will have two way sync for his calendar on my site and his Google Calendar account. How can I go about doing this? Do I store a token for each user or something or how do I do this for each user? Do any of these guides help?: [login to view URL] [login to view URL] Please describe how you will write the PHP and MySQL code.