Connect to google analytics using the google php client and a service account key

google_analytics_via_service_account.php

<?php
/**
 * include via composer Google client lib
 * composer require google/apiclient:^2.0.0@RC
 * include the autoload.php
 *
 * Create a service account key in the google developer console
 * and download the key file into your project above the web root somewhere
 */

require_once '/path/to/your-project/vendor/autoload.php';

/**
 * @return Google_Service_Analytics
 * @throws Exception
 */
function getAnalyticsInstance()
{
    // Creates and returns the Analytics service object.
    // Use the developers console and replace the values with your
    // service account email, and relative location of your key file.
    $key_file_location = 'key_download_from_developer_console.json';
    // Create and configure a new client object.
    $client = new Google_Client();
    $client->setApplicationName('My GA app');
    $analytics = new Google_Service_Analytics($client);
    // Read the generated client_secrets key
    $client->setAuthConfig($key_file_location);
    $scopes = [Google_Service_Analytics::ANALYTICS_READONLY];
    $client->setScopes($scopes);
    if ($client->isAccessTokenExpired()) {
        $client->refreshTokenWithAssertion();
    }
    return $analytics;
}

$analytics = getAnalyticsInstance();
$fromDate  = '2016-01-01';
$toDate    = '2016-01-07';
$results   = $analytics->data_ga->get(
    'ga:{your_google_analytics_profile_id_to_be_queried}',
    $fromDate,
    $toDate,
    'ga:bounceRate,ga:avgSessionDuration,ga:sessions,ga:users,ga:newUsers'
);
$ga        = [];
if ($results && ($rows = $results->getRows())) {
    foreach ($rows as $row) {
        // rows numerically index order as requested in call
        $ga = array(
            'bounceRate'         => (float)$row[0],
            'avgSessionDuration' => (float)$row[1],
            'sessions'           => (int)$row[2],
            'users'              => (int)$row[3],
            'newUsers'           => (int)$row[4]
        );
        // dump output
        var_dump($ga);
    }
}