[security-services] Issues with AuthorityBinding

As part of my pre-last-call review of Core-26, I have a couple of issues
with AuthorityBinding (section 2.4.3.2, lines 750-788).

As described, there is no way to extend this element to allow an
AuthorityBinding to specify other extension types derived from
StatementAbstractType. A SAML implementation that wants to implement a new
form of Statement would not be able to use AuthorityBinding.

One approach would be to change AuthorityKindType to be a qname, and make
the value of the attribute be the actual XML element name of the statement.
So, for a normal SAML AttributeStatement, the AuthorityBinding would look
like:

<AuthorityBinding AuthorityKind="saml:AttributeStatement" .../>

For a hypothetical EnronFinancialStatement, for which the actual SAML
statement would be:

<Statement xsi:type="enron:EnronFinancialStatement"
xmlns:enron="http://enron.com/schemas/finance">
   ...
</Statement>

the AuthorityBinding would look like:

<AuthorityBinding AuthorityKind="enron:EnronFinancialStatement"
xmlns:enron="http://enron.com/schemas/finance" ... />


Of course, the verbosity would be reduced if the xmlns:enron="..." attribute
was applied to an enclosing XML element, so that it didn't need to be
repeated.



The second issue is that there is no way to specify "any". As it currently
stands, the text in core-26 says that AuthorityKind is required, but the
schema leaves it optional. We need to either change the schema to
use="required", or change the text to say that AuthorityKind is optional
and, if unspecified, indicates that the authority will entertain any kind of
query.

 - irving - 


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