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The default PairwiseIdStore implementation is a hash/digest-based approach called "Computed" that avoids the need for a database to store the IDs, but is incapable of reverse-mapping a given identifier (e.g., as part of a SAML attribute query), or revoking or changing the identifier associated with a subject. Tracking back to a subject for debugging purposes generally involves the use of audit logs rather than direct access to a mapping of users. It's not the best approach in the abstract, but it is much simpler to deploy.

To enable the Computed strategy, you must set additional properties:

• idp.persistentId.sourceAttribute

  • A list of attributes from which to derive a "source" key for the subject. The key is used as the hash input, and should be a very stable value for each subject and must never be reassigned later to a different subject. This should be a permanent serial number associated by an IDMS to each account, and not a name-based identifier like a login ID or email address. It should also be technology-neutral; using a GUID generated by an Active Directory is a very bad choice that will lead to problems if you ever change directories.

• idp.persistentId.salt

  • A secret string used as a default salt when hashing the subject key derived from the property above. This is required to prevent trivial attacks to determine the identifier for a given subject, and must be kept secret. Note that leading or trailing whitespace is not trimmed from the property, though using whitespace in the salt is not advisable.

• idp.persistentId.encodedSalt

  • If your salt value contains special characters that Spring won't accept safely, you can work around this by base64-encoding the salt you want to use, and specifying the encoded version in this property instead of the previous property. Do not set both.

  idp.persistentId.encoding

  • Controls the encoding of the generated hash value. Defaults to BASE64 if not set, but new installations set this property to BASE32 to produce values without mixed case.

The attribute used as the source key need not be released (in the sense of an attribute filter policy) to the SP.

Dynamic Salt

There us an advanced option to configure a dynamic salt source using a BiFunction (a Java function object that takes two inputs). If a bean named shibboleth.ComputedIdSaltLookupStrategy is defined, the function will override the value of the salt to use for a request, or if it returns null will suppress generation of a value entirely. This works in combination with the Sparse Override map desribed in the next section (i.e., the map overrides the BiFunction which overrides the default). It is also now legal to only define the BiFunction and omit the global salt if desired.

The bean is of type BiFunction<ProfileRequestContext,PairwiseId>

The intent is that the second argument will supply details about the request such as the subject and relying party, while the first provides full access to request state.

A trivial example that is equivalent to just using a global salt would be:

Code Block
<bean id="shibboleth.ComputedIdSaltLookupStrategy" parent="shibboleth.BiFunctions.Constant"> <constructor-arg> <value>thisisasaltsalthisis</value> </constructor-arg> </bean>

Sparse Overrides

One of the disadvantages of strictly computing IDs is a loss of manageability of the values, particularly the ability to change a value should it become compromised. The IdP includes a feature allowing fine-grained override of the salt value used to generate IDs for specific users and/or relying parties, by means of a Java Map bean, which can be declared in saml-nameid.xml, and by default is named shibboleth.ComputedIdExceptionMap

The Java type of the object is a mouthful: Map<String,Map<String,String>> (i.e., it's a string-keyed map whose values are themselves maps). It's easier to grasp this in practice in the example below.

The primary keys are the names of subjects/users, or an asterisk (*) to signify a wildcard rule.

The values are maps of Relying Party names to salt values. These keys are the names of relying parties or an asterisk (*) as a wildcard, and the values are either a substitute salt string to use, or can be null to block the generation of an ID altogether.

One use for this feature is to maintain an old salt value for a legacy service while relying on a new value for everybody else:

Overriding salt for a single SP

<util:map id="shibboleth.ComputedIdExceptionMap">
	<entry key="*"> <!-- all users -->
		<map>
			<entry key="https://legacysp.example.org/sp" value="legacysalt" />
			<entry key="https://invalid.example.org/sp">
				<null/>	<!-- blocks generation of a value for this SP -->
			</entry>
		</map>
	</entry>
</util:map>

The alternative PairwiseIdStore generates random identifiers on first use and stores them in a database for future use. This has some benefits and addresses some of the limitations of the computed approach, but requires a highly available database accessible to every IdP node and is very difficult (bordering on impossible) to make reliable. Note that it is not possible to implement such a database using asynchronous/unreliable replication. This will lead to conflicts and race conditions, and eventually a risk of errors and duplicate entries. This is the main reason it isn't easy to get working, as most applications simply can't tolerate these kinds of conflicts easily.

The "vanilla" DDL needed for this approach is:

Stored ID Table Definition

CREATE TABLE shibpid (
	localEntity VARCHAR(255) NOT NULL,
	peerEntity VARCHAR(255) NOT NULL,
	persistentId VARCHAR(50) NOT NULL,
	principalName VARCHAR(50) NOT NULL,
	localId VARCHAR(50) NOT NULL,
	peerProvidedId VARCHAR(50) NULL,
	creationDate TIMESTAMP NOT NULL,
	deactivationDate TIMESTAMP NULL,
	PRIMARY KEY (localEntity, peerEntity, persistentId)
); 

You will need to define the table above in your database, and you must define a primary key as shown above or the implementation will not function as intended. The absence of this constraint will normally be detected at startup time and prevent use of the mechanism.

Also ensure that the collation associated with the "localId" column is appropriate for use with the source attribute you specify. An inappropriate collation can render the attribute non-unique. In particular, it has been observed that a case-sensitive collation is needed if using the Active Directory objectSid as the source attribute, to ensure that persistent IDs are uniquely identified. "utf8_bin" has been found to work in this circumstance.

Using this strategy requires setting the properties described earlier, as well as some additional changes:

• The idp.persistentId.generator property needs to be set to "shibboleth.StoredPersistentIdGenerator".

• The idp.persistentId.dataSource property must be set to the name of a DataSource bean you must define. You can place it in saml-nameid.xml if you like (anywhere at the "top" level of the file).

A default feature of the stored strategy is that it uses the computed strategy to produce the initial identifier for each subject, to help with migration. If you don't need that to happen, you can set the idp.persistentId.computed property to an empty value and ignore that feature entirely, but it isn't a terrible idea to leverage this because it hedges your bets. If you find that the stored model is unworkable in practice, you may be able to easily convert back to the computed approach if all your values are compatible with it.

Examples of each type of bean using an unspecified database and the DBCP2 pooling library (included with the IdP) follows. You will need to determine what driver class to plug into the bean definition for your database and the proper URL to use. Always use current drivers when possible; bug fixes for obscure problems tend to be frequent. When in doubt, grab a newer one.

Example persistent ID store beans in saml-nameid.xml

<!-- A DataSource bean suitable for use in the idp.persistentId.dataSource property. -->
<bean id="MyDataSource" class="org.apache.commons.dbcp2.BasicDataSource"
	p:driverClassName="com.example.database.Driver"
	p:url="jdbc:example://localhost/database"
	p:username="shibboleth"
	p:password="foo"
	p:maxIdle="5"
	p:maxWaitMillis="15000"
	p:testOnBorrow="true"
	p:validationQuery="select 1"
	p:validationQueryTimeout="5" />

<!-- A replacement bean suitable for use in the idp.persistentId.generator property. -->
<bean id="MyPersistentIdStore" parent="shibboleth.StoredPersistentIdGenerator"
	p:dataSource-ref="MyDataSource"
	p:queryTimeout="PT2S"
	p:retryableErrors="#{{'23000'}}" />

Advanced Customization

There are a few cases where more advanced customization of the stored approach may be required, and this is accomodated by defining your own custom bean that inherits from "shibboleth.StoredPersistentIdGenerator" and defines any additional bean properties required (see the JDBCPairwiseIdStore javadoc).

The option to define and reference your own bean rather than just supplying a plain DataSource is present to allow you to override the default table and column names used in the data store, the SQL queries used, the timeout, etc, but most of these settings are now accessible in V4.1 via simple Java properties and will not require a bean definition.

Properties defined in saml-nameid.properties to customize various aspects of persistent NameID generation behavior follow: