{  
   "web":{  
      "client_id":"[hash-string].apps.googleusercontent.com",
      "project_id":"calendar-integration-[project-id]",
      "auth_uri":"https://accounts.google.com/o/oauth2/auth",
      "token_uri":"https://accounts.google.com/o/oauth2/token",
      "auth_provider_x509_cert_url":"https://www.googleapis.com/oauth2/v1/certs",
      "client_secret":"[hash-string]",
      "redirect_uris":[  
         "https://www.example.com/oauth2callback"
      ],
      "javascript_origins":[  
         "https://www.example.com"
      ]
   }
}

<?php

namespace App\Helpers;

// Initialise the client.
$client = new Google_Client();
// Set the application name, this is included in the User-Agent HTTP header.
$client->setApplicationName('Calendar integration');
// Set the authentication credentials we downloaded from Google.
$client->setAuthConfig('[private-path]/client_id.json');
// Setting offline here means we can pull data from the venue's calendar when they are not actively using the site.
$client->setAccessType("offline");
// This will include any other scopes (Google APIs) previously granted by the venue
$client->setIncludeGrantedScopes(true);
// Set this to force to consent form to display.
$client->setApprovalPrompt('force');
// Add the Google Calendar scope to the request.
$client->addScope(Google_Service_Calendar::CALENDAR);
// Set the redirect URL back to the site to handle the OAuth2 response. This handles both the success and failure journeys.
$client->setRedirectUri(URL::to('/') . '/oauth2callback');

<?php
// Set state allows us to match the consent to a specific venues
$client->setState($venue->id);
// The Google Client gives us a method for creating the 
$client->createAuthUrl();

<?php
/**
 * Google OAuth2 route
 */
Route::get('oauth2callback', [
    'as' => 'oauth',
    'uses' => 'OAuthController@index'
]);

<?php

public function index(Request $request)
    {
        // Get all the request parameters
        $input = $request->all();

        // Attempt to load the venue from the state we set in $client->setState($venue->id);
        $venue = Venue::findOrFail($input['state']);

        // If the user cancels the process then they should be send back to
        // the venue with a message.
        if (isset($input['error']) &&  $input['error'] == 'access_denied') {
            \Session::flash('global-error', 'Authentication was cancelled. Your calendar has not been integrated.');
            return redirect()->route('venues.show', ['slug' => $venue->slug]);

        } elseif (isset($input['code'])) {
            // Else we have an auth code we can use to generate an access token

            // This is the helper we added to setup the Google Client with our             
            // application settings
            $gcHelper = new GoogleCalendarHelper($venue);

            // This helper method calls fetchAccessTokenWithAuthCode() provided by 
            // the Google Client and returns the access and refresh tokens or 
            // throws an exception
            $accessToken = $gcHelper->getAccessTokenFromAuthCode($input['code']);

            // We store the access and refresh tokens against the venue and set the 
            // integration to active.
            $venue->update([
                'gcalendar_credentials' => json_encode($accessToken),
                'gcalendar_integration_active' => true,
            ]);

            \Session::flash('global-success', 'Google Calendar integration enabled.');
            return redirect()->route('venues.show', ['slug' => $venue->slug]);
        }
    }

{  
   "access_token":"[hash-string]",
   "token_type":"Bearer",
   "expires_in":3600,
   "created":1510917377,
   "refresh_token":"[hash-string]"
}

<?php
// Refresh the token if it's expired.
$client->setAccessToken($venue->gcalendar_credentials);
if ($client->isAccessTokenExpired()) {
    $accessToken = $client->fetchAccessTokenWithRefreshToken($client->getRefreshToken());
    $venue->update([
        'gcalendar_credentials' => json_encode($accessToken),
    ]);
}

<?php

// Load up the helper to initialise the Google Client
$gcHelper = new GoogleCalendarHelper($venue);

// Use the Google Client calendar service. This gives us methods for interacting 
// with the Google Calendar API
$service = $gcHelper->getCalendarService();

// Set over what timeframe we want to grab calendar events
// Dates must be an RFC3339 timestamp with mandatory time zone offset, e.g.,
// 2011-06-03T10:00:00-07:00
$optParams = array(
    'orderBy' => 'startTime',
    'singleEvents' => true,
    'timeMin' => '2011-06-03T10:00:00-07:00',
    'timeMax' => '2011-06-03T10:00:00-23:00',
);

// Poll this venue's Google Calendar
$googleBookings = $service->events->listEvents($calendarId, $optParams);

// Check if we have any events returned
if (count($googleBookings->getItems()) > 0) {

<?php

// Set the start time and date for pushing to Google.
$tz = new DateTimeZone('Europe/London');
$startTime = Carbon::create(
    2017,
    11,
    25,
    10,
    0,
    0,
    $tz
);

// Use the Google date handling provided by the Google Client
$googleStartTime = new Google_Service_Calendar_EventDateTime();
$googleStartTime->setTimeZone($tz);
$googleStartTime->setDateTime($endTime->format('c'));

// Create the calendar event and give a default title.
$event = new Google_Service_Calendar_Event();
$event->setStart($googleStartTime);
// Same process to create end time as we use for the start time above. Code 
// omitted for brevity.
$event->setEnd($googleEndTime);
$event->setSummary('Booking automatically created from Calendar Example');

// Use the Google Client calendar service to push 
$service = $gcHelper->getCalendarService();
$createdEvent = $service->events->insert($calendarId, $event);

// Save the newly created event id against the booking.
if (!empty($createdEvent->id)) {