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More on deref

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Network Working Group P. Masarati
Internet-Draft Politecnico di Milano
Intended status: Standards Track H. Chu
Expires: April 4, 2009 Symas Corp.
October 2008
LDAP Dereference Control
draft-masarati-ldap-deref.txt
Status of this Memo
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Abstract
This document describes the Dereference Control for LDAP. This
control is intended to provide a concise means to collect extra
information related to cross-links present in entries returned as
part of search responses.
Table of Contents
1. Background and Intended Use . . . . . . . . . . . . . . . . . 3
2. The LDAP Dereference Control . . . . . . . . . . . . . . . . . 4
2.1. Control Semantics . . . . . . . . . . . . . . . . . . . . 4
2.2. Control Request . . . . . . . . . . . . . . . . . . . . . 5
2.3. Control Response . . . . . . . . . . . . . . . . . . . . . 5
3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Implementation Notes . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6.1. Object Identifier Registration . . . . . . . . . . . . . . 9
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
8. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Intellectual Property and Copyright Statements . . . . . . . . . . 13
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1. Background and Intended Use
Cross-links between entries are often used to describe relationships
between entries. To exploit the uniqueness of entries naming, these
links are usually represented by the distinguished name (DN) of the
linked entries.
In many cases, DUAs need to collect information about linked entries.
This requires to explicitly dereference each linked entry in order to
collect the desired attributes, resulting in the need to perform a
specific sequence of search operations, using the links as search
base, with a SearchRequest.scope of baseObject [RFC4511].
This document describes a LDAP Control [RFC4511] that allows a DUA to
request the DSA to return specific attributes of linked entries along
with the link, under the assumption that this operation can be
performed by the DSA in a more efficient manner than the DUA would
itself by performing the complete sequence of required search
operations.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. The LDAP Dereference Control
2.1. Control Semantics
This control allows specifying a dereference attribute and a set of
attributes to be dereferenced, as illustrated in Section 2.2. The
dereference attribute's syntax MUST be 1.3.6.1.4.1.1466.115.121.1.12
(DN) [RFC4517]. Each value of the dereference attribute in a
SearchResultEntry SHOULD result in dereferencing the corresponding
entry, collecting the values of the attributes to be dereferenced,
and returning them as part of the control value in the
SearchResultEntry response, in the format detailed in Section 2.3.
The control value may contain dereference attribute values without
any dereferenced attribute values, as detailed in Section 2.3. The
control semantics does not specify whether this is a consequence of a
dangling link or of the application of access restrictions on the
values of the attributes to be dereferenced.
Attribute description hierarchy [RFC4512] SHALL NOT be exploited when
collecting the values of the attributes to be dereferenced. On the
contrary, all of the attribute descriptions in an attribute hierarchy
SHOULD be treated as distinct and unrelated descriptions.
This control is only appropriate for the search operation [RFC4511].
The semantics of the criticality field are specified in [RFC4511].
In detail, the criticality of the control determines whether the
control will or will not be used, and if it will not be used, whether
the operation will continue without returning the control in the
response, or fail, returning unavailableCriticalExtension. If the
control is appropriate for an operation and, for any reason, it
cannot be applied in its entirety to a single SearchResultEntry
response, it MUST NOT be applied to that specific SearchResultEntry
response, without affecting its application to any subsequent
SearchResultEntry response.
Servers implementing this technical specification SHOULD publish the
object identifier deref-oid (IANA assigned; see Section 6) as a value
of the 'supportedControl' attribute [RFC4512] in their root DSE.
This control is totally unrelated to alias dereferencing [RFC4511].
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2.2. Control Request
The control type is deref-oid (IANA assigned; see Section 6). The
specification of the Dereference Control request is:
controlValue ::= SEQUENCE OF derefSpec DerefSpec
DerefSpec ::= SEQUENCE {
derefAttr attributeDescription, ; with DN syntax
attributes AttributeList }
AttributeList ::= SEQUENCE OF attr AttributeDescription
Each derefSpec.derefAttr MUST be unique within controlValue.
2.3. Control Response
The control type is deref-oid (IANA assigned; see Section 6). The
specification of the Dereference Control response is:
controlValue ::= SEQUENCE OF derefRes DerefRes
DerefRes ::= SEQUENCE {
derefAttr AttributeDescription,
derefVal LDAPDN,
attrVals [0] PartialAttributeList OPTIONAL }
PartialAttributeList ::= SEQUENCE OF
partialAttribute PartialAttribute
PartialAttribute is defined in [RFC4511]; the definition is reported
here for clarity:
PartialAttribute ::= SEQUENCE {
type AttributeDescription,
vals SET OF value AttributeValue }
If partialAttribute.vals is empty, the corresponding partialAttribute
is omitted. If all partialAttribute.vals in attrVals are empty, that
derefRes.attrVals is omitted.
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3. Examples
Given these entries:
dn: cn=Howard Chu,ou=people,dc=example,dc=org
objectClass: inetOrgPerson
cn: Howard Chu
sn: Chu
uid: hyc
dn: cn=Pierangelo Masarati,ou=people,dc=example,dc=org
objectClass: inetOrgPerson
cn: Pierangelo Masarati
sn: Masarati
uid: ando
dn: cn=Test Group,ou=groups,dc=example,dc=org
objectClass: groupOfNames
cn: Test Group
member: cn=Howard Chu,ou=people,dc=example,dc=org
member: cn=Pierangelo Masarati,ou=people,dc=example,dc=org
A search could be performed with a Dereference request control value
specified as
{ member, uid }
and the "cn=Test Group" entry would be returned with the response
control value
{ { member, cn=Howard Chu,ou=people,dc=example,dc=org,
{ { uid, [hyc] } } },
{ member, cn=Pierangelo Masarati,ou=people,dc=example,dc=org,
{ { uid, [ando] } } } }
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4. Implementation Notes
This LDAP extension is currently implemented in OpenLDAP software
using the temporary OID 1.3.6.1.4.1.4203.666.5.16 under OpenLDAP's
experimental OID arc.
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5. Security Considerations
The control result MUST NOT disclose information the client's
identity could not have accessed by performing the related search
operations. The presence of a derefRes.derefVal in the response
control, with no derefRes.attrVals, does not imply neither the
existence of nor any access privilege to the corresponding entry. It
is merely a consequence of the read access the client's identity has
on the corresponding value of the derefRes.derefAttr that would be
returned as part of the attributes of a SearchResultEntry response
[RFC4511].
Security considerations described in documents listed in [RFC4510]
apply.
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6. IANA Considerations
6.1. Object Identifier Registration
It is requested that IANA register upon Standards Action an LDAP
Object Identifier for use in this technical specification.
Subject: Request for LDAP OID Registration
Person & email address to contact for further information:
Pierangelo Masarati <ando@OpenLDAP.org>
Specification: (I-D)
Author/Change Controller: IESG
Comments:
Identifies the LDAP Dereference Control request
and response
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7. Acknowledgments
TBD
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8. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4510] Zeilenga, K., "Lightweight Directory Access Protocol
(LDAP): Technical Specification Road Map", RFC 4510,
June 2006.
[RFC4511] Sermersheim, J., "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.
[RFC4517] Legg, S., "Lightweight Directory Access Protocol (LDAP):
Syntaxes and Matching Rules", RFC 4517, June 2006.
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Authors' Addresses
Pierangelo Masarati
Politecnico di Milano
Dipartimento di Ingegneria Aerospaziale
via La Masa 34
Milano 20156
IT
Phone: +39 02 2399 8309
Fax: +39 02 2399 8334
Email: ando@OpenLDAP.org
URI: http://www.aero.polimi.it/masarati/
Howard Y. Chu
Symas Corporation
18740 Oxnard St., Suite 313A
Tarzana, California 91356
USA
Phone: +1 818 757-7087
Email: hyc@symas.com
URI: http://www.symas.com/