Google API Calendar Service Account Example

<?php
...
    private function getMinMaxOfDay($min=true) {
        $date  = new DateTime(date('c'));
        $today = date('j');

        if($min) {
            $today -= 1;
            $date->modify("-$today day");

        }else {
            $maxDay = date('t') - $today;
            $date->modify("$maxDay day");
        }

        return $date->format('c');
    }

    public function actionDemo() {
        $client = new \Google_Client();
        $client->setApplicationName('Demo Calendar Service');

        $clientEmail = 'calendar@demo.iam.gserviceaccount.com';
        $privateKey = join('/', [Yii::getPathOfAlias('application.config'),
            'Demo123.json']);
        $scopes = 'https://www.googleapis.com/auth/calendar.readonly';
        putenv('GOOGLE_APPLICATION_CREDENTIALS=' . $privateKey);

        $client->addScope(\Google_Service_Calendar::CALENDAR_READONLY);
        $client->useApplicationDefaultCredentials();
        $client->setSubject($clientEmail);
        $client->setAuthConfig($privateKey);

        $service = new Google_Service_Calendar($client);
        $optParams = [
            'maxResults'   => 10,
            'orderBy'      => 'startTime',
            'singleEvents' => true,
            'timeMax'      => $this->getMinMaxOfDay(false),
            'timeMin'      => $this->getMinMaxOfDay(),
        ];
        $calendar = $service->events->listEvents('primary', $optParams);
        print_r($calendar->getItems());
    }
...