Wherever you intialise your objects, initialize a new instance of the authorization server and bind the storage interfaces and authorization code grant:
~~~ php
$server = new \League\OAuth2\Server\AuthorizationServer;
When the refresh token grant is enabled, a refresh token will automatically be created with access tokens issued requested using the [authorization code](/authorization-server/auth-code-grant/) or [resource owner password credentials](/authorization-server/resource-owner-password-credentials-grant/) grants.