private void authenticateUsingSaslExternal() throws IOException {
            log("Authenticating using SASL EXTERNAL");
            alreadyTriedSaslExternal = true;
            final Document outbound = DocumentHelper.createDocument();
            final Element root = outbound.addElement(QName.get("auth", "urn:ietf:params:xml:ns:xmpp-sasl"));
            root.addAttribute("mechanism", "EXTERNAL");
            root.setText(Base64.getEncoder().encodeToString(XMPP_DOMAIN.getBytes()));
            send(root.asXML());
        }
Returns 'true' if negotiation was started, false if no negotiation was started.
xmppserver/src/test/java/org/jivesoftware/openfire/session/RemoteInitiatingServerDummy.java