Authentication with Google Calendar API using Server Account and PHP

Question

I'm struggling with this one: I am trying to create an event in a Google Calendar from a PHP script, using a Service Account.

Here’s what I’ve done:

Created a Google Cloud Project
Enabled the Calendar API
Created an OAuth 2.0 Service Account, with Client ID, Email address and Public Key
Downloaded the keyfile and saved this in my website
Shared my Calendar with the Email address created in the Service Account (with Manage Sharing rights)

And here is my code:

<?php

require_once 'google_api_src/Google_Client.php';
require_once 'google_api_src/contrib/Google_CalendarService.php';

const CLIENT_ID = 'xxxxxxxxxxxxx.apps.googleusercontent.com';
const SERVICE_ACCOUNT_NAME = '[email protected]';

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

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

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

// Load the key in PKCS 12 format
$key = file_get_contents(KEY_FILE);
$client->setClientId(CLIENT_ID);

$client->setAssertionCredentials(new Google_AssertionCredentials(
    SERVICE_ACCOUNT_NAME,
    array('https://www.googleapis.com/auth/calendar', "https://www.googleapis.com/auth/calendar.readonly"),
    $key));

$service = new Google_CalendarService($client);

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

?>

I have debugged the code as far as I can, but the token is always set to null after the call to SetAssertionCredentials. There are no PHP errors.

Any idea what is wrong, or how to debug further please? Do I have to make any changes to config.php in the api src folder (I haven’t so far)? Is the Application Name important? What’s it used for?

engeeaitch engeeaitch · Accepted Answer · 2013-12-23T09:34:34

OK - so it turns out that the above code is working fine. My misunderstanding was in thinking that the Google_CalendarService performed the authentication. In fact, the authentication is only performed when an actual call to the calendar is made (such as insert Event).

However, I think that saving the token in the session is in the wrong place - it should be after an action has been performed.

To answer my other questions: No, you don't have to make any changes to config.php. The Application Name can be set to anything (but I don't know what it's used for).

One other problem I came across: I was creating an event using a calendar ID of 'primary'. This sent back a success message, but I could not see the event in the calendar (I only have one calendar for that account). It was only when I changed 'primary' to '[email protected]' that it started working. Sounds like a bug in the API to me?

Authentication with Google Calendar API using Server Account and PHP

2 Answers