I notice that Splice was deprecated as ES (allegedly) did everything Splice did, however one thing Splice supported that ES does not (seem to) is additional auth factors besides username and password. Splice had parameters taxiicertpem and taxicertkey. Is my understanding that ES TAXII downloads do not support these correct, or do I simply need to know the magic post parameters invocation to get this working. Any help much appreciated, but I'm reading the source in parallel and will follow up with the answer if none is forthcoming.
Ok so to save anyone else going hunting, reading contrib/libtaxii/clients.py, it looks like post params is indeed the way to go, thusly:
collection="stuffIwant" authtype="AUTHCERTBASIC" keyfile="/path/to/key.key" cert_file="/path/to/cert.crt" username="blah" password="blahblah"
Hope this helps somebody else!