I am writing a PHP application that's supposed to allow users to add certain events to a private Google Calendar. The calendar is owned by me, and I need a way for PHP to communicate with the calendar API using fixed credentials (everyone can add events using a form on the website, but the calendar itself is not publicly visible).
From what I have read, this is possible using ClientLogin in the v1 API. In the v3 API, however, the available options are OAuth2.0 or the API key. Using the API key doesn't seem to work, since it can only be used for requests that don't require authorization, and OAuth doesn't seem right either, because users are not supposed to access their own calendars, but the one my application uses.
I thought about getting the OAuth token programatically, but that's bound to break sooner or later, since the OAuth dialog can use captchas.
This seems to be such a standard use case — a web application that lets users interact with a single calendar in some predefined ways — yet I can't find any documentation on how to make it happen in the v3 API. Can anyone help me?