PredicateMetadataFilter

The Predicate metadata filter applies an include or exclude rule to each entity in the input if a supplied Predicate<EntityDescriptor> returns true. The predicate may be defined explicitly (via the conditionRef attribute) or implicitly from the child elements.

Contents

Schema

The <MetadataFilter> element and the type Predicate are defined by the urn:mace:shibboleth:2.0:metadata schema, which can be located at http://shibboleth.net/schema/idp/shibboleth-metadata.xsd.

Attributes

Child Elements

If the conditionRef attribute is specified, then only it is used and any child elements are ignored. Otherwise the condition is constructed as one that returns true if:

• The entityID of the candidate matches any of the supplied <Entity> elements OR
• The Name of any ancestor <md:EntitiesDescriptor> element for the candidate matches any of the supplied <Group> child elements OR
• Any <mdattr:EntityAttributes> extension elements associated with the candidate match the supplied <Tag> child elements OR
• Any scripts designated by a <ConditionScript> element return true

Examples

Include a single entity

The following simple example includes at most one entity. This filter intentionally prevents new or unexpected entities from appearing in the metadata feed.

<MetadataFilter xsi:type="Predicate" direction="include" removeEmptyEntitiesDescriptors="true">
	<Entity>https://sp.example.org/trusted-sp</Entity>
</MetadataFilter>

Exclude all entities containing a particular entity attribute

The next example excludes all entities containing a particular entity attribute, presumably because the IdP is the sole authority for this attribute.

<MetadataFilter xsi:type="Predicate" direction="exclude" removeEmptyEntitiesDescriptors="true" trim="true">
    <Tag name="http://macedir.org/entity-category" nameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri">
        <Value>http://idp.example.org/local-category</Value>
    </Tag>
</MetadataFilter>

Exclude all entities subject to a compound implicit condition

Note that implicit conditions may be combined in logical OR fashion. For instance, if any of the conditions in the following example are true, the entity is excluded:

<MetadataFilter xsi:type="Predicate" direction="exclude" removeEmptyEntitiesDescriptors="true" trim="true">
    
    <Entity>https://sp.example.org/untrusted-sp</Entity>
    
    <Tag name="http://macedir.org/entity-category" nameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri">
        <Value>http://idp.example.org/local-category-one</Value>
        <Value>http://idp.example.org/local-category-two</Value>
    </Tag>
    
    <Tag name="http://idp.example.org/entity-category" nameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri">
        <Value>http://idp.example.org/local-category-three</Value>
    </Tag>
</MetadataFilter>

Include all entities based on a regexp applied to the entityID

The core of this is the RegexPredicate. However this takes a string, rather than an EntityID and so we need to navigate to it.  We could of course use jacascript, but the Spring EL Predicate provides a better shorthand.  One injects the RegexPredicate to do the work and use Spring EL to do the navigation.  The result is this Spring Segment

<bean id="the.Metadata.regexp.Pred" class="net.shibboleth.utilities.java.support.logic.RegexPredicate" c:_0="^.*sp1.*" />
<bean id="the.Metadata.Pred" class="net.shibboleth.ext.spring.util.SpringExpressionPredicate"
        p:customObject-ref="the.Metadata.regexp.Pred"
 		c:expression="#custom.apply(#input.getEntityID())" />

Exclude "roleless" entity descriptors

Recall that the following EntityRoleWhiteList filter retains all <md:SPSSODescriptor> elements in the input:

<MetadataFilter xsi:type="EntityRoleWhiteList" xmlns:md="urn:oasis:names:tc:SAML:2.0:metadata">
    <RetainedRole>md:SPSSODescriptor</RetainedRole>
</MetadataFilter>

The previous filter essentially filters all non-SP role descriptors from the input. At the end of that process, if an empty entity descriptor remains (because all of its roles have been removed), the entity itself is removed.

Unfortunately the EntityRoleWhiteList filter may not handle affiliation descriptors as expected. Specifically, an <md:EntityDescriptor> element that contains an <md:AffiliationDescriptor> child element is handled in exactly the same way as an <md:EntityDescriptor> element that contains no role descriptors. That is, if removeRolelessEntityDescriptors is true (which it is by default), both are removed from the input.

A quick fix that preserves any affiliation descriptors in the input is to set removeRolelessEntityDescriptors to false on the EntityRoleWhiteList filter. However, this also prevents truly “roleless” entity descriptors from being removed, which may have a negative impact on memory utilization. A workaround is to use both an EntityRoleWhiteList filter and a Predicate filter, in sequence.

The following filter sequence is a complete replacement for the above EntityRoleWhiteList filter:

<!-- retain SPs only but don’t remove “roleless” entity descriptors -->
<MetadataFilter xsi:type="EntityRoleWhiteList" removeRolelessEntityDescriptors="false" xmlns:md="urn:oasis:names:tc:SAML:2.0:metadata">
    <RetainedRole>md:SPSSODescriptor</RetainedRole>
</MetadataFilter>

<!-- clean up the mess made by the EntityRoleWhiteList filter -->
<MetadataFilter xsi:type="Predicate" direction="exclude" removeEmptyEntitiesDescriptors="true">
    <ConditionScript>
        <Script>
        <![CDATA[
            // an implementation of Predicate<EntityDescriptor>
            //
            // if the predicate function returns true, the entity descriptor
            // is excluded from the output (since direction="exclude").
            //
            // the input argument is of type:
            // org.opensaml.saml.saml2.metadata.EntityDescriptor
            //
            (function (entity) {
                "use strict";

                // check the parameter
                if (entity === null) { return false; }

                // preserve an affiliation descriptor
                if (entity.getAffiliationDescriptor() !== null) { return false; }

                // exclude a "roleless" entity descriptor
                return entity.getRoleDescriptors() === null;
            }(input));
        ]]>
        </Script>
    </ConditionScript>
</MetadataFilter>

Note that removeRolelessEntityDescriptors is set to false on the EntityRoleWhiteList filter, which runs first. The Predicate filter then removes the “roleless” entity descriptors from its input without disturbing the affiliation descriptors (if any).