WebSocket auth example

Using public-key cryptography to support authenticated connection.

Specification

Client:

Connect to server, while also providing the client ID (which will double as the public key), via either the default client_id query parameter, or another query parameter that has been agreed-upon ahead of time. The public key must match a specific format (currently only WebCrypto-raw.EC.P-256 is supported, but more will come, such as P-384, P-512, secp256k1, ed25519, etc.)
Listen for CHALLENGE messages which will contain a payload field
Respond with a CHALLENGE_RESPONSE containing the original payload (payload), and a base64-encoded byte buffer, representing the signature, signature. Optionally, the signature can be prefixed with <signature scheme>, if the signature scheme has more than one possible representation (although, currently, ECDSA emits signatures that are just byte buffer concatenation of the r and s components)
If the challenge response matches, then send a CONNECTED message, and the handshake is now considered complete
- Otherwise, if the signature does not match, then close the connection