- From: Fabian Ritzmann <Fabian.Ritzmann@Sun.COM>
- Date: Fri, 12 Jan 2007 20:22:01 +0200
- To: public-ws-policy@w3.org
- Message-id: <45A7D1C9.4050705@Sun.COM>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=4206
Title
Clarify treatment of policy assertion parameters in compatibility
determination
Description
The treatment of assertion parameters in intersection is ill understood
by policy implementers and policy domains alike. The framework has this
text in section 4.5:
"If a domain-specific intersection processing algorithm is required this
will be known from the QNames of the specific assertion types involved
in the policy alternatives... Assertion parameters are not part of the
compatibility determination defined herein but may be part of other,
domain-specific compatibility processing."
Our understanding is that this means that the default algorithm will
ignore all assertion parameters when computing compatibility unless
otherwise specified by a domain. For example an assertion <Assertion1
parameter1="value1"/> would be compatible with <Assertion1
parameter1="value2"/>. The framework leaves it open if the resulting
intersection set contains <Assertion1 parameter1="value1"/> or
<Assertion1 parameter1="value2"/> or <Assertion1/>.
Looking at the existing public policy domains, WS-SecurityPolicy 1.2
says in the introduction to chapter 2 that it is avoiding the usage of
assertion parameters to allow the default framework intersection
algorithm be used. WS-SecurityPolicy fails to specify how to compute
compatibility in those cases where it could not avoid the usage of
assertion parameters. Here are simple (incomplete) examples of a
parameterized security policy assertion:
<Policy id="p1">
<sp:IssuedToken sp:IncludeToken="http://schemas.xmlsoap.org/ws/2005/07/securitypolicy/IncludeToken/Once"/>
</Policy>
<Policy id="p2">
<sp:IssuedToken sp:IncludeToken="http://schemas.xmlsoap.org/ws/2005/07/securitypolicy/IncludeToken/AlwaysToRecipient"/>
</Policy>
Both policies yield different behavior on the wire. But since
WS-SecurityPolicy does not define any exceptions they would be
considered compatible. It is also left open whether the intersection
result would be:
<Policy id="i1">
<sp:IssuedToken sp:IncludeToken="http://schemas.xmlsoap.org/ws/2005/07/securitypolicy/IncludeToken/Once"/>
</Policy>
or
<Policy id="i2">
<sp:IssuedToken sp:IncludeToken="http://schemas.xmlsoap.org/ws/2005/07/securitypolicy/IncludeToken/AlwaysToRecipient"/>
</Policy>
or
<Policy id="i3">
<sp:IssuedToken/>
</Policy>
Note that policy i3 is equivalent to:
<Policy id="p3">
<sp:IssuedToken sp:IncludeToken="http://schemas.xmlsoap.org/ws/2005/07/securitypolicy/IncludeToken/Always"/>
</Policy>
That means policies i1, i2, i3 would all manifest differently on the wire.
At this point this is an issue with WS-SecurityPolicy, although it is
probable that the language in the framework currently is sufficiently
unclear to cause similar issues with other domains or those that use
complex policies now or in the future. In order to achieve interoperable
results, we could take the following actions:
1. Consider assertion parameters in intersection by default. Two
policy assertions with different parameters[1]
<http://wikihome.sfbay.sun.com/wts/Wiki.jsp?page=PolicySpecIssueMultipleAlternatives#ref-PolicySpecIssueMultipleAlternatives-1>
are not compatible.
2. Alternatively to 1), two assertions whose QNames match shall not
match if either of the assertions contains parameters. Domains may
define more specific match algorithms that can take parameters
into account, and in this case, then the policy engine may use
results from such a processor to determine whether two assertions
that have the same QName, but that also have parameters, actually
match. Policy engines that are not aware of, or are not able to
process domain-specific parameter-matching semantics shall use the
default.[2]
<http://wikihome.sfbay.sun.com/wts/Wiki.jsp?page=PolicySpecIssueMultipleAlternatives#ref-PolicySpecIssueMultipleAlternatives-2>
3. Alternatively to 1), require domains to specify how to treat their
assertion parameters.
4. Provide additional guidance in the guidelines and primer.
Ultimately, the choice between the above action depends on whether it is
worse to choose a policy alternative where some assertions actually
don't match, or to reject a policy alternative that may actually match.
This is an inherent challenge with not having a domain-independent
policy assertion language.
Justification
See description
Target
Framework section 4.5, Guidelines and Primer
Proposal
This proposal addresses the first option, considering parameters in
intersection by default. The other actions would have likely yielded
more changes or introduced incompatibilities for existing domains.
In the framework, change from:
* Two policy assertions are compatible if they have the same type and
* If either assertion contains a nested policy expression, the two
assertions are compatible if they both have a nested policy
expression and the alternative in the nested policy expression of
one is compatible with the alternative in the nested policy
expression of the other.
Assertion parameters are not part of the compatibility determination
defined herein but may be part of other, domain-specific compatibility
processing.
change to:
* Two policy assertions are compatible if they have the same type and
* If either assertion contains parameters and the domain has not
specified how to compute their compatibility, the two assertions
are compatible if they both have the same parameters[1]
<http://wikihome.sfbay.sun.com/wts/Wiki.jsp?page=PolicySpecIssueMultipleAlternatives#ref-PolicySpecIssueMultipleAlternatives-1>
and
* If either assertion contains a nested policy expression, the two
assertions are compatible if they both have a nested policy
expression and the alternative in the nested policy expression of
one is compatible with the alternative in the nested policy
expression of the other.
In the primer, insert this text before the last paragraph in section 3.4:
Policy domains may require that assertion parameters be considered in
order to establish compatibility. The assertion (a1) has a parameter
(p1). This assertion is only compatible with another assertion if the
QNames of the assertions match as well as the QNames and values of the
parameters of both assertions. The assertion (a1) would also be
compatible with another assertion sp:IssuedToken that has no parameter
(p1) because parameter (p1) is the default for this assertion. If
another assertion sp:IssuedToken had a different parameter than (p1) it
would not be compatible with (a1).
Example 3-8. A Policy Expression in Normal Form With a Parameterized Policy Assertion
<Policy>
<ExactlyOne>
<All> <!-- - - - - - - - - - - - - - A Policy Alternative -->
<!-- - - - - - - - - - - - - - - - - - Policy Assertion (a1) -->
<sp:IssuedToken
<!-- - - - - - - - - - - Parameter (p1) to Policy Assertion (p1) -->
sp:IncludeToken="http://schemas.xmlsoap.org/ws/2005/07/securitypolicy/IncludeToken/Always">
¦
</sp:IssuedToken>
</All>
</ExactlyOne>
</Policy>
[#1] The term "same parameters" must still be defined precisely in a
domain-independent way or definition must be deferred to domains. Where
sequences of choices are permitted, for example, parameters may appear
in different orders. The encoding of parameters may differ slightly.
Some parameters may be neglectable.
[#2] We believe this is the current state and has lead to
inconsistencies in WS-SecurityPolicy and potentially other domains. If
this option is chosen, it should be documented whether the intersection
set contains the assertions with all parameters omitted.
--
Fabian Ritzmann
Sun Microsystems, Inc.
Stella Business Park Phone +358-9-525 562 96
Lars Sonckin kaari 12 Fax +358-9-525 562 52
02600 Espoo Email Fabian.Ritzmann@Sun.COM
Finland
Received on Friday, 12 January 2007 18:22:15 UTC