PK Authentication

This will authenticate a user by their public key.

GET `/id` - Gets the node public key

This is then signed, which is then used as a bearer token.

Both the pk and sig are provided as a bearer token, hex-encoded, joined by `:`

The token is authenticated by the client's public key it signs for.

This may require some Axum middleware. We'll also need to look into middleware in order to cache certain things, like pk generation.