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Those are design notes regarding Active Directory Connector (LDAP).

Disclaimer

This page contains opinions of the Evolveum team based on research using public information. This is not an official statement of Evolveum or any other organization (including Microsoft). Those are just personal opinions and notes of our team members. Information on this page may be correct, but it may also contain information that is incomplete, subjective or information that was misunderstood. Please, do not rely on this information. In case that you are aware that this information is wrong, we will appreciate that you let us know so we can correct the information.

AD And LDAP "Compliance"

AD/LDAP connector 1.x and 2.x were built on LDAP principles as much as possible. However, it turns out that AD is not really a good LDAP server. LDAP standards are interpreted in a way that is no way strict (to be politically correct). Therefore the LDAP-based approach fails in many areas. In fact, there were "tweaks" (hacks) in the connector code from the very beginning just to be able to work with AD at all.

The connector is deviating from LDAP standards with almost every release. But the reason for this connector existence is not to be strictly LDAP-compliant. The reason is to work with AD - whatever it takes.

Schema

Perhaps the most problematic part of the AD/LDAP connector is the schema. AD is exposing the schema in a format that resembles standard LDAP schema. However, this is quite a poor approximation. E.g. there are no syntax definition, no matching rules, attributes from auxiliary object classes that are defined on class level are not exposed and so on.

In addition to that poor excuse of an LDAP schema, there is also a "native" (means: proprietary) schema format. This format is similar to standard LDAP format, except that it is quite different. AD connector can use this "native" format since version 2.3. The nativeAdSchema configuration property controls which version of the schema should be used.

EXPERIMENTAL

This "native" AD schema is LDAP-like, but it is different. There are treacherous differences. Different syntaxes are used. Auxiliary object classes are used in a different way. And then there is objectCategory, which is in category of its own (see below). Native AD schema might work well, or it might break. Nobody can be really sure.

Object Class and Object Category

Object class is a critical LDAP concept that determines type of an object. However, contrary to most other LDAP servers, it looks like it was too difficult for AD developers to work with multi-valued objectClass. Therefore AD introduced a proprietary concept of object category. Object category is single-valued and it is somehow determined from object class. It is quite clear how default object category is set, but all the details are not clear (they may to too ghastly to explore).

The important thing is that object class is not properly indexed. Therefore there are several recommendations to use object category for searches instead of object class. This in fact needs to be still combined with object class to get reliable information. Like this:

(&(objectClass=user)(objectCategory=person))

AD connector supports automatic management of objectCategory  since version 2.3. It is controlled by includeObjectCategoryFilter and addDefaultObjectCategory configuration properties. See documentation of those properties for more details. This only works when native AD schema is enabled (see above).

If automatic objectCategory mode is used (addDefaultObjectCategory=true, includeObjectCategoryFilter=true), then the connector will use default object categories specified in native AD schema. This works only if the default object categories are used everywhere and they never change. This mode is unlikely to work reliably in any other circumstances.

See Also

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