@Override
    public byte[] unwrap(byte[] incoming, int offset, int len)
        throws SaslException {
        if(completed) {
            throw new IllegalStateException("PLAIN does not support integrity or privacy");
        } else {
            throw new IllegalStateException("PLAIN authentication not completed");
        }
    }
Unwraps a byte array received from the client. PLAIN supports no security layer.

@throws SaslException if attempted to use this method.
xmppserver/src/main/java/org/jivesoftware/openfire/sasl/SaslServerPlainImpl.java