(PHP Extension) Google Calendar -- Refresh an Expired Access Token

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Demonstrates how to refresh an expired access token. If a Google Calendar REST API call results in a 401 "unauthorized" response, then it is likely the access token expired. An application should be able to automatically refresh the access token with no user interaction and then re-try the request with the newly obtained access token.

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<?php

// The version number (9_5_0) should match version of the Chilkat extension used, omitting the micro-version number.
// For example, if using Chilkat v9.5.0.48, then include as shown here:
include("chilkat_9_5_0.php");

// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// It is assumed we previously obtained an OAuth2 access token.
// This example loads the JSON access token file 
// saved by this example: Get Google Calendar OAuth2 Access Token

$jsonToken = new CkJsonObject();
$success = $jsonToken->LoadFile('qa_data/tokens/googleCalendar.json');
if ($success != true) {
    print 'Failed to load googleCalendar.json' . "\n";
    exit;
}

// The access token JSON looks like this:

// 	{ 
// 	 "access_token": "abac.Ci-ZabcdF37-NUrmSzxbHxTsMbtlN-uPfabcdAQN_2ekzj0s5ofCzRabcdTDMGaa2Q",
// 	 "token_type": "Bearer",
// 	 "expires_in": 3600,
// 	 "refresh_token": "1/lEe5abcdNJ77eOSDBabcdkQGVmDalkwabcdR2Hatbo"
// 	}
// 

$oauth2 = new CkOAuth2();

$oauth2->put_TokenEndpoint('https://www.googleapis.com/oauth2/v4/token');

// Replace these with actual values.
$oauth2->put_ClientId('GOOGLE-CLIENT-ID');
$oauth2->put_ClientSecret('GOOGLE-CLIENT-SECRET');

// Get the "refresh_token"
$oauth2->put_RefreshToken($jsonToken->stringOf('refresh_token'));

// Send the HTTP POST to refresh the access token..
$success = $oauth2->RefreshAccessToken();
if ($success != true) {
    print $oauth2->lastErrorText() . "\n";
    exit;
}

// The response contains a new access token, but we must keep
// our existing refresh token for when we need to refresh again in the future.
$jsonToken->UpdateString('access_token',$oauth2->accessToken());

// Save the new JSON access token response to a file.
$sbJson = new CkStringBuilder();
$jsonToken->put_EmitCompact(false);
$jsonToken->EmitSb($sbJson);
$sbJson->WriteFile('qa_data/tokens/googleCalendar.json','utf-8',false);

print 'OAuth2 authorization granted!' . "\n";
print 'New Access Token = ' . $oauth2->accessToken() . "\n";

?>