$client = new Client($id, $secret, ['version' => '0.3', 'error' => 'array']);
'redirectPreferred' => 'false',
'scopes' => 'payments', // multiple scopes can be added separated with comma
'Request-Id' => uniqid(),
'Redirect-URL' => 'https://your.callback.url' // must match SDK callback url
$response = json_encode($client->auth()->authenticate($attrs));