How to get residence permit for Australian

Hi

Grateful for immigration advice for the following scenario.

John (Australian citizen) wants to join his partner Giovanni (Italian citizen) in Barcelona.

What is the quickest immigration option for getting John work and residence authorisation in Barcelona? Ideas include: some kind of partnership registration, civil union, marriage. Or can an Australian get some kind of work and residence authorisation (without an offer) independent of being linked to an EU national? Working holiday not an option.

Thanks.