Encrypted gRPC

[ygina]

The controller serves a gRPC service. The sensor SDK and hosts currently connect to this service using an http address, but this communication should be encrypted in case there is a passive adversary. Hosts also serve a gRPC service, where communication from the controller should be encrypted. Communication from requests to the host (for data and network accesses) use the local loopback interface. See: https://grpc.io/docs/guides/auth/

• encrypt communication between sensors and controller
• encrypt communication between controller and hosts