Add Event to Google Calendar with PHP

I would like code which will add an event to a Google Calendar calendar. I do not wish to specify the account details in the code as it will be dependent on the user of the site, so therefor the Google Calendar of the current website user would be used. I'm looking for a simple step-by-step instructions and working code. The code will be used on a hosted website so I do not have access to the root server, so any addins will need to be installed by simple ftp.