ensure client can be used with UTF-16 formatted strings for keys

We have a requirement that the client be able to work with UTF-16 encoded strings.

In the ideal case, I think, this would just be if the environment were UTF-16 we simply encode the bytes when sending the key as UTF-16, and no special setup is required. If that's not possible, then we need to ensure that passing a UTF-16 encoded string as a key flows through to the server and back unharmed.

Tests needed.