I'm creating a calendar tool for a client. He has his work calendars in a Google account, which I have access to. I'll be using the Google Calendar API for the tool, but I'm new to Google APIs and the OAuth stuff. I'll be using PHP. Do I need to use an OAuth2 Service Account, or should I make a regular OAuth2 Web Application Client ID from that Google account?

In case this information is helpful, the tool I will be making will do this: 1) Allow my client to fill out a form which will create a new calendar and populate it with several events. 2) Send out an email to a mailing list twice a week listing changes that have been made to these calendars.

I'll also be making a page that displays the iframes for each calendar, so his clients may see them even if they do not have a Google account.