[wss] SAML binding and Urn:ietf:rfc:3075

section "3.4 Proof-of-Possession of Security Tokens" of the SAML binding 
lists
the XML Signature authentication method "Urn:ietf:rfc:3075" as a mandatory
subject confirmation mechanism.

I think this "authentication mechanism" should be removed from the list of
mandatory SAML subject confirmation mechanisms.

Assertions containing a "holder-of-key" subject confirmation method indicate
that the sender of the assertion must demonstrate knowledge of some key 
data.
Presumably, such knowledge could be demonstrated by various means; xml
signature being one, although what must be signed would likely also need to
qualified (by the msg receiver). In addition to xml-signature, the same
holder-of-key assertion could likely be confirmed by another type of cipher
operation such as xml encryption.

I believe the specification of how knowledge of the key is demonstrated
should NOT be conveyed in the assertion, but rather in information like
that being proposed by the QOP work, where a service description might
describe the proof or proofs that are required of the message sender.

Thoughts/comments?

Ron