The Person Attributes Group Store ("PAGS")


The PAGS makes user attributes retrieved by PersonDirectory appear to be group memberships.  (PersonDirectory initializes IPersons with attributes retrieved from one or more sources of directory information, including, for example LDAP.  For more information, see the PersonDirectory documentaton.)

PAGS computes entity memberships by testing the value of selected IPerson attributes.  Like PersonDirectory, the PAGS retrieves information one user at a time.  As a result, it can answer inquiries about what groups a particular IPerson or group member belongs to, but it cannot answer inquiries about what entity members are contained by a given group. 

Can do:

contains()
find()
findContainingGroups()

Can't do: 

findEntitiesForGroup()

Although PAGS groups cannot answer their entity members, they are aware of their member groups.  So they can also do:
 
findMemberGroupKeys()
findMemberGroups()

This will usually suffice for authorization, so the PAGS can be thought of as an authorization-oriented group store.  Since PersonDirectory supplies information about IPersons and not about ChannelDefinitions or other portal entities, a further limitation is that the PAGS can only contain memberships associating IPerson group members with IPerson groups. 

Configuring the Store.  The contents of the store is declared in a configuration document, properties/groups/PAGSGroupStoreConfig.xml. The dtd is as follows:

 <!-- A Group-Store is made up of 0 or more groups. -->
<!ELEMENT Group-Store (group*)>

<!ELEMENT group (group-key,group-name,description,selection-test?,members?)>
<!-- A group key must be unique within the document.  A group-name need not be. -->

<!ELEMENT group-key (#PCDATA)>
<!ELEMENT group-name (#PCDATA)>
<!ELEMENT group-description (#PCDATA)>

<!ELEMENT selection-test (test-group+)>
<!--
  A selection-test element determines if a person is a member of a group.  It is
  composed of one or more test-group elements whose results are OR-ed together.
  If a group does not contain a selection-test, it may have member groups but not
  member entities. 
-->

<!ELEMENT test-group (test+)>
<!--
  A test-group element is made up of 1 or more test elements whose results are
  AND-ed together. 
-->

<!ELEMENT test (attribute-name,tester-class,test-value)>
<!--
  A test element contains the name of the attribute whose value is to be tested
  (attribute-name), the class that is to perform the test (tester-class), and the
  value to be compared to the attribute value (test-value).  
-->
<!ELEMENT attribute-name (#PCDATA)>
<!ELEMENT tester-class (#PCDATA)>
<!ELEMENT test-value (#PCDATA)>

<!ELEMENT members (member-key*)>
<!-- The optional members element contains keys of member groups. -->
<!ELEMENT member-key (#PCDATA)>

The configuration lets you do 2 things: (i) declare IEntityGroups with key, name, description and member group keys, and (ii) declare the tests that determine if an IPerson is a member of a group.  Since a group need not contain any member groups, the <members> element is optional. Since a group need not contain any member entities,  the <selector-test> element is also optional.

Tests.  Each of the tests to be applied to an IPerson is described in a <test> element, which consists of 3 required sub-elements, the name of the test class, the name of the attribute to be tested, and the value against which the attribute is to be tested by the tester class. In the example below, the test is true if the String value of the attribute "sn" equals "Jones". 

        <test>
          <attribute-name>sn</attribute-name>
          <tester-class>org.jasig.portal.groups.pags.testers.StringEqualsTester</tester-class>
          <test-value>Jones</test-value>
        </test>

 The PAGS currently ships with 8 tester classes, and you can easily create your own.  Each tester class must implement the IPersonTester interface, which consists of a single method:

public interface IPersonTester {
    public boolean test(IPerson person);
}

The following tester classes (all in the package org.jasig.portal.groups.pags.testers) come with PAGS:

IntegerEQTester
 Converts attribute and test value to ints. Attribute must be EQ to the test value.  In the event of a  NumberFormatException, the test fails (true for all Integer testers.)
IntegerGETester
 Attribute must be GE test value.
IntegerGTTester
 Attribute must be GT test value.
IntegerLETester
 Attribute must be LE test value.
IntegerLTTester
 Attribute must be LT test value.
RegexTester
 Attribute must match a regular expression.  Do not include the delimiter.
StringEqualsIgnoreCaseTester
 String comparison ignoring case
StringEqualsTester
 String comparison


Test Groups.  Individual tests are aggregated into test groups, and their results are AND-ed together, so all tests in a test group must return true for the test group to return true.  A test group is described by a <test-group> element.  If there is more than 1 <test-group> element, the results of the test groups are OR-ed together, so if any one test group returns true, the tests return true.  A true result means that the candidate IPerson is a member of the group. 

The following group element defines an IEntityGroup whose key is "2".  The entity members of group "2" are required to have a given name that is between 1 and 5 characters long.  This test is performed by comparing the attribute givenName with a regular expression.  The group has a single member group, whose key is "3".  Group "3" must also be defined in the configuration document.  See the sample PAGSGroupStoreConfig.xml that ships with uPortal for additional examples. 

  <group>
    <group-key>2</group-key>
    <group-name>Short First Names</group-name>
    <group-description>Portal users whose first names are between 1 and 5 characters long</group-description>
    <selection-test>
      <test-group>
        <test>
          <attribute-name>givenName</attribute-name>
          <tester-class>org.jasig.portal.groups.pags.testers.RegexTester</tester-class>
          <test-value>^.{1,5}$</test-value>
        </test>
      </test-group>
    </selection-test>
    <members>
      <member-key>3</member-key>
    </members>
  </group>
Multi-valued attributes.  The testers that come with PAGS will OR the tests of successive values of a multi-valued attribute, so if any value satisfies the test, the test returns true.  You can override this behavior in a custom tester. 

Caching of group store information.  Because the groups structure defined in the PAGS is invarient, an instance of each group, including the keys of its containing groups, is cached by the store on start-up.  These cached instances are dealt out to satisfy all requests to the store for groups.  As a result, any change to the store configuration (via PAGSGroupStoreConfig.xml) requires restarting the group service, which generally means restarting the portal.  By contrast, memberships for an IPerson group member are cached for the life of the corresponding user's portal session.  As a result, if an IPerson's attributes change, these new attributes -- and any group memberships they imply -- will be visible on next log in. 

Recursive Testing.  If one PAGS group (the child group) belongs to another PAGS group (the parent group), then an IPerson member of the child group must also pass the test(s) required for membership in the parent group.  This is a more restrictive contract than the group system in general requires, where membership in a group only means that some relationship exists between a group and its members.  Here, when an entity group member belongs to a group, it means that the underlying entity has some specific attribute value(s).  The PAGS enforces this by testing the entity for membership in all its parent groups, which means you can nest the testing of entity members.  For example, assume a group named named "employees" requires status equal to "employed" and a group named "seniors" requires age GE 65.  If "seniors" is a member of "employees", then any IPerson member of "seniors" is required to have both age GE 65 and status equal to "employed". 

Checklist for implementing PAGS:
Running in uPortal 2.1.x.  The PAGS has been successfully ported to uPortal 2.1.x by Ken Weiner with the following steps (thank you Ken):

 1. Copy all the source code from the org.jasig.portal.groups.pags and org.jasig.portal.groups.pags.testers packages.
 2. Copy org.jasig.portal.security.IPerson.
 3. Copy org.jasig.portal.security.provider.RestrictedPerson.
 4. Copy org.jasig.portal.services.PersonDirectory. Change the constructor of this class from private to public access.
 5. Copy org.jasig.portal.security.PersonFactory.  Also copy the following property into portal.properties:

org.jasig.portal.security.PersonFactory.guest_user_name=guest

 6. Modify org.jasig.portal.RDBMUserLayoutStore, adding the following method to the inner class SystemUser:

public Object[] getAttributeValues (String key) {return null;}

 7. Modify org.jasig.portal.security.provider.PersonImpl, adding the method with the following signature:

public Object[] getAttributeValues (String key)

    and replacing the method with the following signiture:

public Object getAttribute (String key)

    Also add the following supporting import statement:

import java.util.List;

 8. Copy properties/groups/PAGSGroupStoreConfig.xml.
 9. Copy webpages/dtd/PAGSGroupStore.dtd.
10. Modify compositeGroupServices.xml, adding the PAGS group store implementation configuration.

last revised: 04/07/2004, d.e.