Bug 1025779 - Generation (at POST /call-url)  and retrieval (GET /calls/{token}) of the call-url should require/provide an optional issuer parameter

We are talking about the person who issues the token, so the callee.

In the case where you're initiating the call without a call-url (when doing a post on /calls), I think we want to know who is calling, so that would be the callee id.

+1 for naming the params differently on these two URLs