LDAP attrs by class: Requesting Attributes by Object Class in the Lightweight Directory Access Protocol
Request all attributes of a directory object class in one go.
Zeilenga, K., "Requesting Attributes by Object Class in the Lightweight Directory Access Protocol", RFC 4529, DOI 10.17487/RFC4529, June 2006, <https://www.rfc-editor.org/info/rfc4529>.
@misc{rfc4529,
series = {Request for Comments},
number = 4529,
howpublished = {RFC 4529},
publisher = {RFC Editor},
doi = {10.17487/RFC4529},
url = {https://www.rfc-editor.org/info/rfc4529},
author = {K. Zeilenga},
title = {{Requesting Attributes by Object Class in the Lightweight Directory Access Protocol}},
pagetotal = 6,
year = 2006,
month = jun,
} RFC text
Contents
Network Working Group K. Zeilenga
Request for Comments: 4529 OpenLDAP Foundation
Category: Informational June 2006
Requesting Attributes by Object Class in the
Lightweight Directory Access Protocol (LDAP)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
The Lightweight Directory Access Protocol (LDAP) search operation
provides mechanisms for clients to request all user application
attributes, all operational attributes, and/or attributes selected by
their description. This document extends LDAP to support a mechanism
that LDAP clients may use to request the return of all attributes of
an object class.
Table of Contents
1. Background and Intended Use .....................................1
2. Terminology .....................................................2
3. Return of all Attributes of an Object Class .....................2
4. Security Considerations .........................................3
5. IANA Considerations .............................................3
6. References ......................................................4
6.1. Normative References .......................................4
6.2. Informative References .....................................4
1. Background and Intended Use
In the Lightweight Directory Access Protocol (LDAP) [RFC4510], the
search operation [RFC4511] supports requesting the return of a set of
attributes. This set is determined by a list of attribute
descriptions. Two special descriptors are defined to request all
user attributes ("*") [RFC4511] and all operational attributes ("+")
[RFC3673]. However, there is no convenient mechanism for requesting
pre-defined sets of attributes such as the set of attributes used to
represent a particular class of object.
This document extends LDAP to allow an object class identifier to be
specified in attributes lists, such as in Search requests, to request
the return of all attributes belonging to an object class. The
COMMERCIAL AT ("@", U+0040) character is used to distinguish an
object class identifier from an attribute descriptions.
For example, the attribute list of "@country" is equivalent to the
attribute list of 'c', 'searchGuide', 'description', and
'objectClass'. This object class is described in [RFC4519].
This extension is intended primarily to be used where the user is in
direct control of the parameters of the LDAP search operation, for
instance when entering an LDAP URL [RFC4516] into a web browser, such
as <ldap:///dc=example,dc=com?@organization?base>.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in BCP 14
[RFC2119].
DSA stands for Directory System Agent (or server).
DSE stands for DSA-specific Entry.
3. Return of All Attributes of an Object Class
This extension allows object class identifiers to be provided in the
attributes field of the LDAP SearchRequest [RFC4511] or other request
values of the AttributeSelection data type (e.g., attributes field in
pre/post read controls [ReadEntry]) and/or <attributeSelector>
production (e.g., attributes of an LDAP URL [RFC4516]). For each
object class identified in the attributes field, the request is to be
treated as if each attribute allowed by that class (by "MUST" or
"MAY", directly or by "SUP"erior) [RFC4512] were itself listed.
This extension extends the <attributeSelector> [RFC4511] production
as indicated by the following ABNF [RFC4234]:
attributeSelector =/ objectclassdescription
objectclassdescription = ATSIGN oid options
ATSIGN = %x40 ; COMMERCIAL AT ("@" U+0040)
where <oid> and <options> productions are as defined in [RFC4512].
The <oid> component of an <objectclassdescription> production
identifies the object class by short name (descr) or object
identifier (numericoid). If the value of the <oid> component is
unrecognized or does not refer to an object class, the object class
description is to be treated as an unrecognized attribute
description.
The <options> production is included in the grammar for extensibility
purposes. An object class description with an unrecognized or
inappropriate option is to be treated as unrecognized.
Although object class description options and attribute description
options share the same syntax, they are not semantically related.
This document does not define any object description option.
Servers supporting this feature SHOULD publish the object identifier
(OID) 1.3.6.1.4.1.4203.1.5.2 as a value of the 'supportedFeatures'
[RFC4512] attribute in the root DSE. Clients supporting this feature
SHOULD NOT use the feature unless they know that the server supports
it.
4. Security Considerations
This extension provides a shorthand for requesting all attributes of
an object class. Because these attributes could have been listed
individually, introduction of this shorthand is not believed to raise
additional security considerations.
Implementors of this LDAP extension should be familiar with security
considerations applicable to the LDAP search operation [RFC4511], as
well as with general LDAP security considerations [RFC4510].
5. IANA Considerations
Registration of the LDAP Protocol Mechanism [RFC4520] defined in this
document has been completed.
Subject: Request for LDAP Protocol Mechanism Registration
Object Identifier: 1.3.6.1.4.1.4203.1.5.2
Description: OC AD Lists
Person & email address to contact for further information:
Kurt Zeilenga <kurt@openldap.org>
Usage: Feature
Specification: RFC 4529
Author/Change Controller: Kurt Zeilenga <kurt@openldap.org>
Comments: none
This OID was assigned [ASSIGN] by OpenLDAP Foundation, under its
IANA-assigned private enterprise allocation [PRIVATE], for use in
this specification.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4234] Crocker, D., Ed. and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", RFC 4234, October 2005.
[RFC4510] Zeilenga, K., Ed., "Lightweight Directory Access
Protocol (LDAP): Technical Specification Road Map", RFC
4510, June 2006.
[RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access
Protocol (LDAP): The Protocol", RFC 4511, June 2006.
[RFC4512] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): Directory Information Models", RFC 4512, June
2006.
[RFC4516] Smith, M., Ed. and T. Howes, "Lightweight Directory
Access Protocol (LDAP): Uniform Resource Locator", RFC
4516, June 2006.
[X.680] International Telecommunication Union -
Telecommunication Standardization Sector, "Abstract
Syntax Notation One (ASN.1) - Specification of Basic
Notation", X.680(2002) (also ISO/IEC 8824-1:2002).
6.2. Informative References
[RFC3673] Zeilenga, K., "Lightweight Directory Access Protocol
version 3 (LDAPv3): All Operational Attributes", RFC
3673, December 2003.
[RFC4519] Sciberras, A., Ed., "Lightweight Directory Access
Protocol (LDAP): Schema for User Applications", RFC
4519, June 2006.
[RFC4520] Zeilenga, K., "Internet Assigned Numbers Authority
(IANA) Considerations for the Lightweight Directory
Access Protocol (LDAP)", BCP 64, RFC 4520, June 2006.
[ReadEntry] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP) Read Entry Controls", RFC 4527, June 2006.
[ASSIGN] OpenLDAP Foundation, "OpenLDAP OID Delegations",
http://www.openldap.org/foundation/oid-delegate.txt.
[PRIVATE] IANA, "Private Enterprise Numbers",
http://www.iana.org/assignments/enterprise-numbers.
Author's Address
Kurt D. Zeilenga
OpenLDAP Foundation
EMail: Kurt@OpenLDAP.org
Full Copyright Statement
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AI ELI5
On this page
§1The Shorthand Problem
The Lightweight Directory Access Protocol (LDAP) lets clients search a directory and specify which attributes to return. Two special shortcuts exist: '*' for all user attributes and '+' for all operational attributes. However, there is no easy way to say 'give me all attributes for a person' or 'give me all attributes for a network machine' without listing every attribute name individually.
This is inconvenient when clients (like web browsers) let users manually type LDAP search URLs or when provisioning tools need to fetch standard attributes for common object types.
Directory entries come in kinds: a person, a machine, an organization. Each kind has its own set of fields. LDAP has shortcuts for 'all user fields' or 'all system fields', but not for 'all person fields'.
§2The Object Class Selector
RFC 4529 extends LDAP search requests to accept object class identifiers prefixed with the '@' character (called COMMERCIAL AT in the RFC). When a client requests an attribute named '@person', the server treats it as if the client had listed all attributes defined for the person object class, whether they are required by 'MUST' or optional by 'MAY' directives.
The object class can be specified by its short name (like '@person') or by its object identifier number (OID). If the server does not recognize the object class, it treats it as an unknown attribute and behaves accordingly.
You write '@person' instead of 'name, email, phone, office, ...' and the directory knows to return all the standard person fields. The @ sign tells it you mean an object class, not a single field.
§3Server Support and Extensibility
Servers that support this feature publish an object identifier (OID) 1.3.6.1.4.1.4203.1.5.2 in their 'supportedFeatures' attribute. Clients that support the feature should check for this OID before using the '@' syntax.
The RFC defines an optional 'options' field for future extensibility (for example, to request only required attributes or only optional attributes), though no options are defined in this RFC.
Servers announce if they support this feature. Clients can ask first: 'Do you handle @person?' and only use it if the server says yes.
§4Primary Use Cases
The RFC identifies the main use case as user-directed LDAP searches, such as when a web browser prompts a user to type an LDAP URL. For example, a user might enter 'ldap:///dc=example,dc=com?@organization?base' to retrieve all attributes of the organization object class without needing to know or type every field name.
This is also useful in administration and provisioning where tools want to fetch a standard set of attributes for common entry types.
This is mainly for when a person types an LDAP search URL in a web browser or when a tool wants to say 'show me a standard organization entry without me spelling out every field'.
§5Security and Status
RFC 4529 is informational. The RFC notes that this extension does not raise additional security concerns beyond standard LDAP search security, because the attributes that can be requested are exactly the ones that could be listed individually.
The OID 1.3.6.1.4.1.4203.1.5.2 was assigned by the OpenLDAP Foundation under its private enterprise allocation and has been registered with IANA.
This feature is safe because it just saves you from typing. It does not reveal anything or change access rules. It is an informational RFC that describes a helpful LDAP extension.