There are two use cases:
- Default Registered Role
- Captive Portal Authentication
If you are just using default role assignment (ie. Enable Captive Portal Authentication is unchecked and a Registered Role is assigned), then there is nothing special you would need to do. The AP will handle it automatically. If you are using captive portal, then you just need to check Allow new clients to use the network when vWLAN is down and assign a role.