negotiate! (Net::SSH::Authentication::Agent)

        # File lib/net/ssh/authentication/agent.rb, line 80
    80:     def negotiate!
    81:       # determine what type of agent we're communicating with
    82:       type, body = send_and_wait(SSH2_AGENT_REQUEST_VERSION, :string, Transport::ServerVersion::PROTO_VERSION)
    83:
    84:       if type == SSH2_AGENT_VERSION_RESPONSE
    85:         raise NotImplementedError, "SSH2 agents are not yet supported"
    86:       elsif type != SSH_AGENT_RSA_IDENTITIES_ANSWER1 && type != SSH_AGENT_RSA_IDENTITIES_ANSWER2
    87:         raise AgentError, "unknown response from agent: #{type}, #{body.to_s.inspect}"
    88:       end
    89:     end