 it presented one or
      <tt>:required</tt> to verify the server's certificate
      and fail if an invalid or no certificate was presented.
      Defaults to <tt>*make-ssl-client-stream-verify-default*</tt>
      which is initialized to <tt>:required</tt>
    </p>
    <p>
      <tt>hostname</tt> if specified, will be sent by client during TLS negotiation,
      according to the Server Name Indication (SNI) extension to the TLS.
      When server handles several domain names, this extension enables the se