using rpcz with curve: encryption and role-based authencation

[mhaberler]

really a question for suggestions than a bug, and much of it might be a zeromq question rather than rpcz proper, but anyway:

I plan to use rpcz in www.machinekit.io
right now we dont use any encryption/authentication ontop of zeromq, but eventually we'll have to, including role-based access of clients to methods

any suggestions how to do this?
anybody needing something along these lines so we can share the effort?