How to insert an event as - Out Office

Question

I'm currently working with Google-Calendar-API and trying to insert a new "Out Of Office" event in my google calendar.

I'm using the following code to insert an event:

    $client = getClient();
    $service = new Google_Service_Calendar($client);

    $calendarId     = 'primary';
    $event = new Google_Service_Calendar_Event([
            'summary'       => 'Summery Tets',
            'description'   => 'DescriptionTest',
            'start'         => ['dateTime' => '2019-01-14T09:00:00-07:00'],
            'end'           => ['dateTime' => '2019-01-14T10:00:00-07:00'],
            'reminders'     => ['useDefault' => false],
            'transparency'  => 'opaque',
        ]);
    $results = $service->events->insert($calendarId, $event);

and it inserts an event - no problems, but i want it to be a "Out Of Office"-Event. I have been reading the calendar API DOC, but cant find anything about the out of office "function"

API Doc: https://developers.google.com/calendar/