Track performance of custom traffic sources using Google Analytics

I would like to assign a custom keyword to a particular traffic source and track the traffic I receive from it using Google Analytics. Is something like that possible with WordPress?

For example, here's a link: mashable.com/2015/05/16/snapchat-millennials-entitlement/?utm_cid=mash-com-fb-pete-link

Notice the "utm_cid" that's added to it towards the end. Is there a direct way or a hack to achieve this for WordPress posts?