Leverage OpenCloud public keys for distributing Syndicate slice secrets

[jcnelson]

As part of beta, syndicated.py pulls its shared slice secret directly from OpenCloud, and it gets sent in the clear. This is obviously insecure.

We don't yet know what the public-key infrastructure for OpenCloud will be like.

• If there is a sliver-specific key pair, then the Syndicate Observer should encrypt the sliver credentials with it. Syndicated.py should look up the sliver private key to decrypt it.
• If there is a slice-specific key pair, then the Syndicate Observer should encrypt the slice credentials with it. Syndicated.py should look up the slice private key to decrypt it.
• If there is a node-specific key pair, then the Syndicate Observer should encrypt the sliver credentials with it. Syndicated.py should look up the node private key to decrypt it.

ASIDE: what I think should happen is there should be a node key pair, with the public key registered to OpenCloud. Upon instantiation, the sliver should generate a key pair, and send the public key signed by the node private key to OpenCloud, for other services (like the Syndicate Observer) to look it up.

[jcnelson]

We can do better: Leverage Passcards and a cryptocurrency miner to do this instead.

[muneeb-ali]

Yes, that'd be awesome!

[jcnelson]

We'll deploy Blockstack DNS at each site.

[jcnelson]

The automounter now has a pluggable interface for handling multiple different authentication mechanisms. Will go ahead and close this here, and deal with this particular issue on the automounter issue tracker.