That very much is a question that has to be answered with “it depends.” It depends on who you are, what you're working on, and the circumstances.
For example, all of our ambassadors are empowered to speak. In fact, all of our officials are empowered to speak. One has to take into consideration whether someone is in a position to say something meaningful about that issue, because in many cases policy has yet to be decided, so speaking out wouldn't be helpful to anybody in that regard.
Normally there's no approval process, as far as I'm aware, but there is certainly a consultative process. Anybody who's considering speaking to the media wants to be sure they're apprised of all the information that would be useful in that regard. That requires consultation with a number of parts of the department, including our communications branch, which has very often the best overview of an issue.