byte SSH_AGENT_EXTENSION
string extension id
... extension-specific data follows ...
`extension id' will of course be allocated in the same way all other
SSH string ids are done: anything with an @ in it belongs to the
owner of the domain after the @. That way, I can safely invent
extensions to the agent protocol in a namespace I can be sure nobody
else will attempt to re-use for other purposes.
My vision of this message type is that it can be sent from client to
agent _or_ from agent to client, depending on the extension. An
agent should not be the first to send it, so a client can rely on
not seeing strange unexpected extension messages in response to its
requests; but if the client sends an extension message, the agent
might need to respond with other extension messages if no existing
response message is appropriate.