[security-services] Core changes for ISSUE DS-14-19

[Scott Cantor <cantor.2@osu.edu>]

I took an AI to submit changes to core-28 for DS-14-19, the removal of
AdviceElement/AdviceType. Here is suggested replacement text that also
cleans up the text after the removal of AssertionSpecifier. I also
changed the minOccurs on the choice to 1 because it makes no sense to
have an empty Advice element since its optional anyway.

Replace section 2.3.2.2 (lines 657-682) with the following:

2.3.2.2. Element <Advice>

The <Advice> element contains any additional information that the issuer
wishes to provide. This information MAY be ignored by applications
without affecting either the semantics or the validity of the assertion.
The <Advice> element contains a mixture of one or more <Assertion>
elements, <AssertionIDReference> elements, and elements in other
namespaces, with lax schema validation in effect for these other
elements.

Following are some potential uses of the <Advice> element:

	Include evidence supporting the assertion claims to be cited,
either directly (through incorporating the claims) or indirectly (by
reference to the supporting assertions).

	State a proof of the assertion claims.

	Specify the timing and distribution points for updates to the
assertion.

The following schema fragment defines the <Advice> element and its
AdviceType complex type:

<element name="Advice" type="saml:AdviceType"/>
<complexType name="AdviceType">
   <choice minOccurs="1" maxOccurs="unbounded">
      <element ref="saml:AssertionIDReference"/>
      <element ref="saml:Assertion"/>
      <any namespace="##other" processContents="lax"/>
   </choice>
</complexType>

-- Scott