I am using service account with key.p12 cert to access google calendar API. However, it cannot access any user\'s calendar in the domain. I did follow the steps to Delegatin
As you pointed out, you need to share the existing calendar with the service account
@developer.gserviceaccount.com
(You can find the account in question under the credentials tab in Google Developers Console, it's called 'EMAIL ADDRESS')
Hope it helps.