Currently the /goal command opens a dialog screen allowing the broadcaster to set a channel goal.
Params would be:
type - MUST be Followers, or Subscribers (if the channel is able to have subs)
goal: number of followers/subs for goal
description - optional string
color - one of Twitchs preset color options
Response would be either an error, or success along with the URL for the browser source.
Preceeding uservoice for this.