access to undefined property aud

[Matthias Merz]

In current version 2.1.0 we do get (on requests with old/invalid tokens):

PHP Notice:  Undefined property: stdClass::$aud in [...]/vendor/amzn/login-and-pay-with-amazon-sdk-php/PayWithAmazon/Client.php on line 306
PHP Stack trace:
...
PHP  11. PayWithAmazon\Client->getUserInfo() [...]/AmazonGateway.php:153

this is caused by Client.php not checking for errors and unconditionally accessing $data->aud:

public function getUserInfo($accessToken)
    ...
    $response = $httpCurlRequest->httpGet($url);
    $data       = json_decode($response);
    
    if ($data->aud != $this->config['client_id']) {
        // The access token does not belong to us
        throw new \Exception('The Access token entered is incorrect');
    }

You should also catch something like this:

    if (isset($data->error) && $data->error === 'invalid_token') {
        throw new \Exception('The Access token entered is incorrect');
    }

because in that case, $data->aud will not exist. And maybe also throw an exception if $data is empty because of json parsing errors ;-)