private static void sendChallenge(Session session, byte[] challenge) {
        sendElement(session, "challenge", challenge);
    }
Handles the SASL authentication packet. The entity may be sending an initial
authentication request or a response to a challenge made by the server. The returned
value indicates whether the authentication has finished either successfully or not or
if the entity is expected to send a response to a challenge.

@param session the session that is authenticating with the server.
@param doc the stanza sent by the authenticating entity.
@return value that indicates whether the authentication has finished either successfully
        or not or if the entity is expected to send a response to a challenge.
xmppserver/src/main/java/org/jivesoftware/openfire/net/SASLAuthentication.java