ASN1TaggedObject constructed = (ASN1TaggedObject) is.readObject();
            if ( constructed == null || constructed.getTagClass() != BERTags.APPLICATION ||
                    !(constructed.getBaseObject() instanceof  ASN1Sequence) )
                throw new IOException("Malformed SPNEGO token " + constructed);

            ASN1Sequence vec = (ASN1Sequence) constructed.getBaseObject();