Source of Campaigns in API


I am using the API to retrieve specific information, mainly the source of goals, top pages etc… for a customized dashboard for a customer.

The campaigns are retrievable with Referrers.getCampaigns but the source is lacking. With expanded=1, the keywords appear but I do not need them. I cannot find information about the source.
How can I extract the source of a campaign? What would be the API method?

An old ticket exists and does not have an answer either.

Thank you