public function authorize(Req $req, Res $res, $args)
{
$grant_type = $req->getInput('grant_type');
$client_id = $req->getServerParam('PHP_AUTH_USER');
$client_secret = $req->getServerParam('PHP_AUTH_PW');
$oauth = new Oauth();
$result = $oauth->get_token($client_id, $client_secret, $grant_type);
return $res->authorize_output($result);
}