Google api client php access token not working - php

Question

I am using "google api client php" to get access token using service account json base key file. But i am getting access token null. My sample code is
$client = new \Google_Client();
$client->setApplicationName('My App');
putenv('GOOGLE_APPLICATION_CREDENTIALS=path-to-the-key.json');
$client->useApplicationDefaultCredentials();
$client->setScopes(['https://www.googleapis.com/auth/analytics.readonly']);
$client->authorize();
$token = $client->getAccessToken();
echo $token; // null

Answer 1

I was solved my problem by developing own php code from google documentation. I use sign JWT payload using Guzzle HTTP Client to get access token. Here is the doc
My implementation:
public static function base64url_encode($data) {
return rtrim(strtr(base64_encode($data), '+/', '-_'), '=');
}
public static function getJwtAssertion($private_key_file)
{
$json_file = file_get_contents($private_key_file);
$info = json_decode($json_file);
$private_key = $info->{'private_key'};
//{Base64url encoded JSON header}
$jwtHeader = self::base64url_encode(json_encode(array(
"alg" => "RS256",
"typ" => "JWT"
)));
//{Base64url encoded JSON claim set}
$now = time();
$jwtClaim = self::base64url_encode(json_encode(array(
"iss" => $info->{'client_email'},
"scope" => "https://www.googleapis.com/auth/analytics.readonly",
"aud" => "https://www.googleapis.com/oauth2/v4/token",
"exp" => $now + 3600,
"iat" => $now
)));
$data = $jwtHeader.".".$jwtClaim;
// Signature
$Sig = '';
openssl_sign($data,$Sig,$private_key,'SHA256');
$jwtSign = self::base64url_encode($Sig);
//{Base64url encoded JSON header}.{Base64url encoded JSON claim set}.{Base64url encoded signature}
$jwtAssertion = $data.".".$jwtSign;
return $jwtAssertion;
}
public static function getGoogleAccessToken($private_key_file)
{
$result = [
'success' => false,
'message' => '',
'token' => null
];
if (Cache::has('google_token')) {
$result['token'] = Cache::get('google_token');
$result['success'] = true;
return $result;
}
if(!file_exists($private_key_file)){
$result['message'] = 'Google json key file missing!';
return $result;
}
$jwtAssertion = self::getJwtAssertion($private_key_file);
try {
$client = new Client([
'base_uri' => 'https://www.googleapis.com',
]);
$payload = [
'grant_type' => 'urn:ietf:params:oauth:grant-type:jwt-bearer',
'assertion' => $jwtAssertion
];
$response = $client->request('POST', 'oauth2/v4/token', [
'form_params' => $payload
]);
$data = json_decode($response->getBody());
$result['token'] = $data->access_token;
$result['success'] = true;
$expiresAt = now()->addMinutes(58);
Cache::put('google_token', $result['token'], $expiresAt);
} catch (RequestException $e) {
$result['message'] = $e->getMessage();
}
return $result;
}
Now call it:
$googleToken = getGoogleAccessToken($KEY_FILE_LOCATION);

Answer 2

I used similar type of client to get access token but that was for google sheets.
This would be same like that. So I'm sharing my google sheets code snippet here.
<?php
if (!function_exists('curl_reset'))
{
function curl_reset(&$ch)
{
$ch = curl_init();
}
}
require_once __DIR__ . '/goog/vendor/autoload.php';
define('APPLICATION_NAME', 'Google Sheets API PHP Quickstart');
define('CREDENTIALS_PATH', __DIR__ . '/sheets.googleapis.com-php-quickstart.json');
define('CLIENT_SECRET_PATH', __DIR__ . '/client_secret.json');
// If modifying these scopes, delete your previously saved credentials
// at ~/.credentials/sheets.googleapis.com-php-quickstart.json
define('SCOPES', implode(' ', array(
Google_Service_Sheets::SPREADSHEETS)
));
if (php_sapi_name() != 'cli') {
throw new Exception('This application must be run on the command line.');
}
/**
* Returns an authorized API client.
* #return Google_Client the authorized client object
*/
function getClient() {
$client = new Google_Client();
$client->setApplicationName(APPLICATION_NAME);
$client->setScopes(SCOPES);
$client->setAuthConfig(CLIENT_SECRET_PATH);
$client->setAccessType('offline');
// Load previously authorized credentials from a file.
$credentialsPath = CREDENTIALS_PATH;
if (file_exists($credentialsPath)) {
$accessToken = json_decode(file_get_contents($credentialsPath), true);
} else {
// Request authorization from the user.
$authUrl = $client->createAuthUrl();
printf("Open the following link in your browser:\n%s\n", $authUrl);
print 'Enter verification code: ';
$authCode = trim(fgets(STDIN));
// Exchange authorization code for an access token.
$accessToken = $client->fetchAccessTokenWithAuthCode($authCode);
// Store the credentials to disk.
if(!file_exists(dirname($credentialsPath))) {
mkdir(dirname($credentialsPath), 0700, true);
}
file_put_contents($credentialsPath, json_encode($accessToken));
printf("Credentials saved to %s\n", $credentialsPath);
}
$client->setAccessToken($accessToken);
// Refresh the token if it's expired.
if ($client->isAccessTokenExpired()) {
$client->fetchAccessTokenWithRefreshToken($client->getRefreshToken());
file_put_contents($credentialsPath, json_encode($client->getAccessToken()));
}
return $client;
}
So when you call getClient function in a php script in command line it will generate a link to verify the user in browser after that it will provide an code which you have to place in the command line. Then it will generate the access token which can be reused later.