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User and Group Synchronization : The Default Implementation

Default Implementation of Sync API


The default implementation (SyncManagerImpl) is intended for use in an OSGi-base repository setup: it tracks all SyncHandler registered via OSGi.

It can be used in non-OSGi environments by passing a org.apache.jackrabbit.oak.spi.whiteboard.Whiteboard to the constructor.


The DefaultSyncHandler comes with a set of configuration options that allow to specify the synchronization behavior (see below). Depending on the configuration it chooses between two different SyncContext implementations.


Oak provides the following implementations of the SyncContext interface:

  • DefaultSyncContext: base implementation that synchronizes external user and group accounts into the repository
  • DynamicSyncContext: derived implementation that provides special handling for external groups.

All users/groups synchronized by this context will get the following properties set. These properties allow to run separate task for periodical update and make sure the authorizables can later on be identified as external users.

  • rep:externalId : This allows to identify the external users, know the associated IDP and distinguish them from others.
  • rep:lastSynced : Sync timestamp to mark the external user/group valid for the configurable time (to reduce expensive syncing). Once expired, they will be validated against the 3rd party system again.

NOTE: Since Oak 1.5.8 the system-maintained property rep:externalId is protected and can not be altered using regular JCR and Jackrabbit API, irrespective of the permission setup of the editing session. For backwards compatibility this protection can be turned off. See OAK-4301 for further details.

The DefaultSyncContext is exported as part of the ‘basic’ package space and may be used to provide custom implementations.


Extending from the DefaultSyncContext this implementation that provides special handling for external groups in case the Dynamic Group Membership option is enabled in the Configuration.

In addition to the properties mentioned above this implementation will create a multivalued STRING property that caches the group principal names of the external user accounts:


The DefaultSyncResultImpl is exported as part of the ‘basic’ package space providing a simple SyncResult implementation based on a status and a DefaultSyncedIdentity.


The DefaultSyncedIdentity is exported as part of the ‘basic’ package space. It maps the ID of a synchronized user/group account to the external identity references represented by ExternalIdentityRef.

Dynamic Group Membership

As of Oak 1.5.3 the default sync handler comes with an addition configuration option that allows enabling dynamic group membership resolution for external users. Enabling dynamic membership in the DefaultSyncConfig will change the way external groups are synchronized (see also OAK-4101).

The details and effects on other security related modules are described in section Dynamic Membership and Dynamic Groups.

Dynamic Groups

As of Oak 1.46.0 there exists the option to leverage Dynamic Membership in combination with a new Dynamic Groups configuration option (see also OAK-9803). If both options are enabled external groups will continue to be synchronized into the repository making sure the user-group relationship can still be inspected using Jackrabbit User Management API without losing the benefits of the dynamic membership. See section Dynamic Membership and Dynamic Groups for details and comparison.

XML Import

The protected nature of the rep:externalPrincipalNames is also reflected during XML import of user accounts:

External users with a rep:externalPrincipalNames property will get regularly imported. However, any non-system driven import will omit the rep:externalPrincipalNames and additional remove the rep:lastSynced property in order to force a re-sync of the external user by the system upon the next login or when triggered through the JMX console. Depending on the User Dynamic Membership configuration value on the target system the sync will then result in a full sync of group membership or will re-create the rep:externalPrincipalNames property.



As of Oak 1.5.3 a dedicated Validator implementation asserts that the protected, system-maintained property rep:externalPrincipalNames is only written by the internal system session.

This prevents users to unintentionally or maliciously manipulating the information linking to the external identity provider in particular their external identity and the set of external group principals associated with their account.

Additionally, the validator asserts the consistency of the properties defined with external user/group accounts.

Code Message
0070 Attempt to create, modify or remove the system property ‘rep:externalPrincipalNames’
0071 Attempt to write ‘rep:externalPrincipalNames’ with a type other than Type.STRINGS
0072 Property ‘rep:externalPrincipalNames’ requires ‘rep:externalId’ to be present on the Node.
0073 Property ‘rep:externalId’ cannot be removed if ‘rep:externalPrincipalNames’ is present.

If protection of the rep:externalId property is enabled (since Oak 1.5.8) the validator performs the following checks:

Code Message
0074 Attempt to add, modify or remove the system maintained property ‘rep:externalId’.
0075 Property ‘rep:externalId’ may only have a single value of type STRING.
Protecting synchronized external users/groups

If protection of synchronized external users/groups is enabled (since Oak 1.44.0) an additional validator is present which either warns upon or prevents creation, modification and removal of external identities that have been synchronized into the repository with the following exception:

  • System sessions and configured service user principals (see systemPrincipalNames option) are exempted from the protection
  • Other security related content present with a given synced user/group can still be written given the editing session has the required permissions (e.g. adding access control content or removing token nodes).

The protection aims to prevent inconsistencies between the IDP (source of truth), and the synchronized user/group accounts in particular group membership and properties.

The following constraint violations will be reported:

Code Message
0076 Attempt to add property ‘%s’ to protected external identity node ‘%s’
0076 Attempt to modify property ‘%s’ at protected external identity node ‘%s’
0076 Attempt to delete property ‘%s’ from protected external identity node ‘%s’
0076 Attempt to add protected external identity ‘%s’
0076 Attempt to add node ‘%s’ to protected external identity node ‘%s’
0076 Attempt to remove protected external identity ‘%s’
0076 Attempt to remove node ‘%s’ from protected external identity
Enforcing dynamic groups

If user.dynamicMembership is enabled together with group.dynamicGroups a separate validator will be present to make sure no members are added to the dynamic groups through regular API calls (Group.addMember(Authorizable) and Group.addMembers(String...).

Note, that groups that have been synchronized prior to dynamic synchronization also subject to this validator and can no longer have new members added. They will eventually become dynamic upon synchronization of their members, which will wipe out previously written membership information.

The following constraint violation exceptions will be raised upon persisting changes when new members have been added to a dynamic external group:

Code Message
0077 “Attempt to add members to dynamic group ‘%s’ at ‘%s’”


Configuration of the DefaultSyncHandler

The default SyncHandler implementations are configured via DefaultSyncConfig:

Name Property Description
Sync Handler Name Name of this sync configuration. This is used to reference this handler by the login modules.
User auto membership user.autoMembership List of groups that a synced user is added to automatically
User Expiration Time user.expirationTime Duration until a synced user gets expired (eg. ‘1h 30m’ or ‘1d’).
User Membership Expiration user.membershipExpTime Time after which membership expires (eg. ‘1h 30m’ or ‘1d’).
User membership nesting depth user.membershipNestingDepth Returns the maximum depth of group nesting when membership relations are synced. A value of 0 effectively disables group membership lookup. A value of 1 only adds the direct groups of a user. This value has no effect when syncing individual groups only when syncing a users membership ancestry.
User Dynamic Membership user.dynamicMembership Enabling dynamic membership for external users.
User Enforce Dynamic Membership user.enforceDynamicMembership If enabled together with user.dynamicMembership previously synced membership information will be migrated to dynamic membership upon user sync. Otherwise it takes no effect.
User Path Prefix user.pathPrefix The path prefix used when creating new users.
User property mapping user.propertyMapping List mapping definition of local properties from external ones. eg: ‘profile/email=mail’.Use double quotes for fixed values. eg: 'profile/nt:primaryType=“nt:unstructured”
Disable missing users user.disableMissing By default, users that no longer exist on the external provider will be locally removed. Set this property to true to disable them instead and have them re-enabled if they become available again.
Group auto membership group.autoMembership List of groups that a synced group is added to automatically
Group Expiration Time group.expirationTime Duration until a synced group expires (eg. ‘1h 30m’ or ‘1d’).
Group Path Prefix group.pathPrefix The path prefix used when creating new groups.
Group property mapping group.propertyMapping List mapping definition of local properties from external ones.
Group ‘Dynamic Groups’ group.dynamicGroups Only takes effect in combination with user.dynamicMembership and will result in external groups being synced as dynamic groups.

Automatic Membership with AutoMembershipConfig

Since Oak 1.42.0 (OAK-9463) the auto-membership behavior can be extended to allow for conditional group membership based on characteristics of a given synced external identity. In addition to configuration options group.autoMembership and user.autoMembership that apply for all groups/users, the new interface AutoMembershipConfig can be implemented to defined fine-grained membership e.g. based on external group membership or on particular properties defined with a given external user.

The DefaultSyncHandler is tracking services implementing AutoMembershipConfig that match the handler by name. If present the additional membership defined by the AutoMembershipConfig, will be reflected upon default and dynamic sync together with the original, ‘global’ auto-membership configuration.

Configuration of the ‘Apache Jackrabbit Oak External PrincipalConfiguration’

Please note that the ExternalPrincipalConfiguration (“Apache Jackrabbit Oak External PrincipalConfiguration”) comes with a dedicated RepositoryInitializer, which requires the repository to be (re)initialized once the module oak-auth-external is installed.

The recommended way to assert a proper init, is to add ‘’ as additional value to the requiredServicePids configuration option of the SecurityProviderRegistration (“Apache Jackrabbit Oak SecurityProvider”).

See section Introduction to Oak Security for further details on the SecurityProviderRegistration.

The ExternalPrincipalConfiguration defines the following configuration options:

Name Property Description Values
External Identity Protection protectExternalId Enables protection of the system maintained rep:externalId properties true,false
External User and Group Protection protectExternalIdentities Enables protection of synchronized external users/groups accounts (since Oak 1.44.0). None: no protection (default),
Warn: log warnings,
Protected: protection enabled
System Principal Names systemPrincipalNames Names of additional ‘SystemUserPrincipal’ instances that are excluded from the protection check (since Oak 1.44.0) true,false