Handle a few common macOS errors, as well as gRPC unimplemented errors, and
return more user-friendly messages in their place.
gravitational/teleport.e#514
Implement native macOS methods required by device enrollment, namely methods to
Create/Get the device key, Sign challenges with it, and to collect device data
(aka serial number).
The implementation is rather similar to lib/auth/touchid, but simpler in a few
aspects:
1. Device keys don't require user interaction (as in they don't cause a touch ID
prompt); and
2. There exists, at most, a single device key at all times.
I've added a tiny refactor to reuse Apple public key parsing from touchid, plus
some changes so touchid doesn't break in the face of unexpected keys (which the
device key didn't cause, per se, but my experiments getting to it did).
gravitational/teleport.e#514
Alan Parra