How do I connect to the Google Calendar API without the oAuth authentication?

If I'm not wrong, they've launched Service Account for this now: https://developers.google.com/accounts/docs/OAuth2ServiceAccount

Edit:

Here's the modification from their Prediction API

    session_start();
    require_once "google-api-php-client/src/Google_Client.php";
    require_once "google-api-php-client/src/contrib/Google_CalendarService.php";

    const CLIENT_ID = '...';
    const SERVICE_ACCOUNT_NAME = '...';

    // Make sure you keep your key.p12 file in a secure location, and isn't
    // readable by others.
    const KEY_FILE = '...';

    $client = new Google_Client();
    $client->setApplicationName("...");


    if (isset($_SESSION['token'])) {
     $client->setAccessToken($_SESSION['token']);
    }

    // Load the key in PKCS 12 format (you need to download this from the
    // Google API Console when the service account was created.
    $key = file_get_contents(KEY_FILE);
    $client->setAssertionCredentials(new Google_AssertionCredentials(
        SERVICE_ACCOUNT_NAME,
        array('https://www.googleapis.com/auth/calendar', "https://www.googleapis.com/auth/calendar.readonly"),
        $key)
    );

    $client->setClientId(CLIENT_ID);
    $service = new Google_CalendarService($client);

    //Save token in session
    if ($client->getAccessToken()) {
      $_SESSION['token'] = $client->getAccessToken();
    }

    //And now you can use the code in their PHP examples, like: $service->events->listEvents(...)

Also take a look here:

https://github.com/googleapis/google-api-php-client#authentication-with-service-accounts

After creating a service account you can authenticate without the user prompt for adding items to a calendar your service owns.

I have the same problem. I found this 3 part tutorial that makes exactly what you want . Web page for bookings
You create a web page that writes directly into your own calendar (not the users) and that is why users don't have to give you permission to access their calendar.
This solution works for me, but you have to manage it directly with REST.

I am looking for a way to use google api php client because it seems a bit simpler. But I have not yet found a way to how to properly edit the google-api-php-client/src/config.php file to work in a way where you authenticate yourself not the actual user, because you need access to your calendar. If anyone has an idea or a script that would do that I would be very grateful.