通过Google Cal API发出检索内容的问题

Working on a WP plugin. It's end purpose is to serve as an inspection calendar for home inspectors. We're working with a Google Calendar that is already loaded full of events.

I am authenticating via Oauth2 & a Service account. The plugin needs only to access the inspection company's data, no other private user data.

Here's the code:

    // Set up identity ------------------------------------.
    $client_email = "XXXXXX@XXXXXXXXXX.iam.gserviceaccount.com";
    $private_key = file_get_contents( EC_INSPECT_CAL_INC . "/HE_Web_1.p12" );
    $scope = [ "https://www.googleapis.com/auth/calendar","https://www.googleapis.com/auth/calendar.readonly","https://www.google.com/calendar/feeds" ];
    $credentials = new \Google_Auth_AssertionCredentials(
        $client_email,
        $scope,
        $private_key
    );


    // Build Config Obj ------------------------------------.
    $config = new \Google_Config();
    $config->setClassConfig('Google_Cache_File', array('directory' => EC_INSPECT_CAL_INC . '/tmp/cache'));


    // Instantiate Client Connection ------------------------.
    $client = new \Google_Client( $config );
    $client->setAssertionCredentials( $credentials );
    if( $client->getAuth()->isAccessTokenExpired() )
        $client->getAuth()->refreshTokenWithAssertion();

    $service            = new \Google_Service_Calendar( $client );
    $calendarList       = $service->calendarList->listCalendarList();

    while( true )
    {

        foreach( $calendarList->getItems() as $calendarListEntry )
        {

            // get events 
            $events = $service->events->listEvents( $calendarListEntry->id );

            foreach( $events->getItems() as $event )
                        echo "-----".$event->getSummary() . "<br>";

        }


        $pageToken      = $calendarList->getNextPageToken();
        if( !$pageToken ) break;


        $optParams      = array('pageToken' => $pageToken);
        $calendarList   = $service->calendarList->listCalendarList($optParams);

    }
}

If I var_dump the following:

var_dump( $service->calendarList->listCalendarList() );

It results in:

array(0) { }

My wife would like me to stop cursing in front of the dogs, but I can't seem to figure out what I'm overlooking. The calendar is loaded with content, and I (AFAIK) am authenticating ... So where's the goods??