Close all active sessions and return a <not-authorized/> stream error when cancelling a user account

From XEP-77:

The host MUST perform the remove based on the 'from' address of the IQ set, usually matching based on bare JID (<user@domain>). If the entity cancels its registration with a server (not a service), the server SHOULD then return a <not-authorized/> stream error and terminate all active sessions for the entity.

Thanks Guus.