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Internet-Draft E. Stokes
LDAP Extensions WG D. Byrne
Intended Category: Standards Track B. Blakley
Expires: 15 October 1999 IBM
15 April 1999
Access Control Model for LDAP
<draft-ietf-ldapext-acl-model-02.txt>
STATUS OF THIS MEMO
This document is an Internet-Draft and is in full
conformance with all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet
Engineering Task Force (IETF), its areas, and its working
groups. Note that other groups may also distribute
working documents as Internet-Drafts. Internet-Drafts are
draft documents valid for a maximum of six months and may
be updated, replaced, or obsoleted by other documents at
any time. It is inappropriate to use Internet- Drafts as
reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be
accessed at http://www.ietf.org/shadow.html.
Comments and suggestions on this document are encouraged.
Comments on this document should be sent to the LDAPEXT
working group discussion list:
ietf-ldapext@netscape.com
ABSTRACT
This document describes the access control model for the
Lightweight Directory Application Protocol (LDAP)
directory service. It includes a description of the
model, the LDAP controls, and the extended operations to
the LDAP protocol. A separate document defines the
corresponding application programming interfaces (APIs).
RFC2219 [Bradner97] terminology is used.
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1. Introduction
The ability to securely access (replicate and distribute)
directory information throughout the network is necessary
for successful deployment. LDAP's acceptance as an
access protocol for directory information is driving the
need to provide an access control model definition for
LDAP directory content among servers within an enterprise
and the Internet. Currently LDAP does not define an
access control model, but is needed to ensure consistent
secure access across heterogeneous LDAP implementations.
The major objective is to provide a simple, but secure,
highly efficient access control model for LDAP while also
providing the appropriate flexibility to meet the needs
of both the Internet and enterprise environments and
policies. This document defines the model and the
protocol extensions (controls and extended operations).
A separate document defines the corresponding application
programming interfaces (APIs).
2. Overview
Access Control mechanisms evaluate requests for access to
protected resources and make decisions about whether
those requests should be granted or denied. In order to
make a grant/deny decision about a request for access to
a protected resource, an access control mechanism needs
to evaluate policy data. This policy data describes
security-relevant characteristics of the requesting
subject and the rules which govern the use of the target
object.
This proposal defines the protocol elements for
transmission of this access control policy data in an
LDAP environment and an attribute that defines the access
control mechanism in effect for a given part of the LDAP
namespace. The instantiation of an access control model
at the directory server is not defined in this document.
By defining only what flows on the wire allows existing
access control mechanisms to be used at the directory
server.
No mechanisms are defined in this document to control
access to access control information or for storage of
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access control information at the server; this is vendor
dependent.
A separate requirements document for access control
exists. The access control model used the requirements
documents as a guideline for the development of this
specification and are reflected in this specification to
the extent that the working group could agree on an
access control model.
The access control model defines
- A wire protocol for interoperability: The existing
LDAP protocol flows for add, delete, modify, etc are
used to manipulate access control information.
There are additional LDAP controls and extended
protocol operations defined to further help
management of access control information:
getEffectiveRights, listSubjectRights, and
specifyCredentials.
- LDAP Directory Interchange Format (LDIF) for
application portability: The LDIF is defined for
access control information (ACI). This LDIF is also
used as input to the LDAP APIs so access control
information can be addressed uniformly independent
of how that information is stored and addressed at
the server.
- A set of attributes to identity the access control
mechanisms supported by a server.
Encoding of access control information on the wire is per
the LDAPv3 specifications.
3. Terminology
An "access control list" contains the access control
policy information controlling access to an object or
collection of objects. An access control list consists
of a set of access control list entries.
An "access control list entry" defines a single subject
security attribute's granted rights for the objects
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governed by the access control list to which it belongs.
The "access control policy information" (acpi) for an
object or a collection of objects defines which subject
security attributes entitle a subject to which granted
rights. The access control policy information for an
object is stored in an access control list.
An "access decision" is a boolean-valued function which
answers the question: "can the subject with these subject
security attributes perform this operation on this
object?"
An "access decision function" is an algorithm which makes
an access decision based on subject security attributes,
access control policy information, an object identifier,
and an operation name (possibly augmented by additional
contextual information).
An "access decision function interface" is a programmatic
interface through which applications can request an
access decision.
An "access identity" is an identity which is used by an
access decision function to make an access decision.
An "audit identity" is an identity which does not, in the
absence of additional information, enable a party
receiving and examining it to determine which subject it
belongs to.
A "credential" is a collection of subject security
attributes.
"effective rights" are the complete set of rights a
subject is entitled to based on all access control lists
which apply to a specific object and based on all of the
subject's security attributes.
"granted rights" are the complete set of rights an access
control list entitles a subject to based on a specific
subject security attribute.
A "group" is a privilege attribute asserting a subject's
membership in the collection of subjects whose name is
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that of the group.
An "identity" is a subject security attribute which is
unique to a single subject.
An "object" is the target of operations in an information
system.
An "operation" is the result of executing the code
accessed through a named entry point in an information
system.
An "operation name" is the name of the entry point
through which an operation is invoked in an information
system.
A "privilege attribute" is a subject security attribute
which may be shared by several subjects.
"required rights" are the complete set of rights needed
to authorize a requester to perform a specific operation
on an object of a specific type.
A "right" is the basic unit of access control policy
administration. For each object type in an information
system, a security administrator defines a set of
required rights for each operation. For each object in
the system, a security administrator defines a set of
granted rights for each subject security attribute. When
an access decision is required, an access decision
function checks to make sure that the requester's subject
security attributes have been granted all required rights
needed to perform the requested operation on the
specified target object.
A "role" is a privilege attribute asserting a subject's
organizational position and entitlement to perform the
operations appropriate to that organizational position.
A "subject" is an entity which intiates actions in an
information system.
A "subject security attribute" is a defined property
which is used by a security policy evaluation system to
make policy decisions.
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4. The Model
4.1 Access Control Activity Lifecycle
The access control proposal described in this draft
addresses four activities:
- Creation of subject security attribute information
and access control policy information
- Retrieval of subject security attribute information
at the time an access request is made
- Evaluation of access requests against policy,
resulting in an access decision
- Replication of access control policy information
from one server to another
4.2 Access Control Information Model
This document does not define formats for storage of
access control information; it does define the
operational semantics of access control operations.
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The diagram below illustrates the componentry of an LDAP
system and the placement of the function specified in
this draft.
+-------------+
| Application |
+-------------+
+--------+
| LDAP |
| Client |
+--------+
|
|
| <-- LDAP Extended Access Control
Controls
| or Extended Access Control
Operations
v
+-----------------------------+
| LDAP Server (e.g. SLAPD) |
+-----------------------------+
. |
. |
. |
. |
v v
+----------+ +-----------+
| Access | | |
| Control |<.....| Datastore |
| Manager | | |
+----------+ +-----------+
LDAP clients use the controls and extended operations
specified in this document to administer access control
policy enforced by LDAP servers. Servers may store
access control information in any way they choose. In
particular, servers may use the access control mechanisms
of their datastores to store and enforce LDAP access
control, or they may implement access control managers
external to their datastores. Datastores and external
access control managers may implement any access control
rule syntax and semantics they choose, as long as the
semantics is compatible with that defined in the section
titled "Operational Semantics of Access Control
Operations" (found after the control and extended
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operation definition).
The access control administration mechanisms specified in
this document are neutral with respect to policy
inheritance mechanisms, explicit vs. implicit denial,
and group nesting.
4.3 Bind and Credentials
A bind authenticates a principal to the directory. A
principal is represented by a DN. A principal has a set
of credentials that are used for determining whether
access to resources specified in ldap operations. These
credentials may be pushed to the server by the client or
may be pulled by the server from the directory data.
Credentials may be local with respect to the server. If
not local (owned by another server or administrative
scope), then the server may decide to define a trust
model that states how to evaluate the trust of a
credential at bind time. The definition of such a trust
model is outside the scope of this document.
5. Access Control Information Schema
5.1 Attributes
5.1.1 Root DSE Attribute for Access Control Mechanism
The following attribute may be included in the Root DSE.
(<OID to be assigned>
NAME 'supportedACIMechanisms'
DESC list of access control mechanisms supported
by this directory server
SYNTAX LDAPOID
)
Two access control mechanisms are defined by this
document:
LDAPv3 <OID to be assigned>
X500 <OID to be assigned>
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Other vendor access control mechanisms can be defined (by
OID) and are the responsibility of those vendors to
provide the definition and OID.
5.1.2 Subschema Attribute for Access Control Mechanism
A given naming context must provide information about
which access control mechanism is in effect for that
portion of the namespace. The following attribute must
be in each subschema entry associated with a naming
context whose access control mechanism is different from
adjacent naming contexts supported by that directory
server.
- aCIMechanism lists the value (an OID) that defines
the access control mechanism in effect for the scope
of that subschema entry
5.2 Other Defined Parameters/OIDs
5.2.1 Rights Families and Rights
The following rights families are defined:
LDAPv3 <OID to be assigned>
X500 <OID to be assigned>
Other parties can (and will) define other rights
families. It is the responsibility of those parties to
provide the definition and OID.
5.2.1.1 LDAPv3 Rights Family
Access rights can apply to an entire object or to
attributes of the object. Each of the LDAP access rights
are discrete. One permission does not imply another
permission. The rights may be ORed together to provide
the desired rights list.
Rights which apply to attributes are:
1 Read Read attribute values
2 Write Write attribute values
4 Search Search entries with specified attributes
8 Compare Compare attributes
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Rights that apply to an entire object are:
16 Add Add an object below this object
32 Delete Delete this object
Rights that apply to the object to which the directory
object points are:
64 Manage Perform a privileged operation; used to
restrict access to operations which
read or write especially sensitive data
128 Use Execute; useful in controlling access to
the objects referred to by directory
entries than in controlling access to
the directory entries themselves
256 Get Get retrieves the attribute values
512 Set Set writes the attribute values
5.2.1.2 The X.500 Rights Family
<define the rights for X.500>
5.2.2 DN Types
The following DN Types are defined:
- access-id, OID=<OID to be assigned>
- group, OID=<OID to be assigned>
- role, OID=<OID to be assigned>
access-id, group, and role MUST be supported. An acess-
id is a non-collection (non-group and non-role objects)
DN that can be authenticated.
Other parties can (and will) define other DN Types. It
is the responsibility of those parties to provide the
definition and OID.
6. Access Control Parameters for LDAP Controls & Extended
Operations
This section defines the parameters used in the access
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control LDAP controls and extended operations in this
document.
targetDN specifies the initial directory entry in DN
syntax on which the control or extended operation is
performed.
whichObject specifies whether the access control
information which is get/set is for the target directory
entry (ENTRY) or the target directory entry and its
subtree (SUBTREE).
rightsFamily specifies the family of rights that will be
get/set for the control or extended operation performed.
A rights family has a defined set of rights.
rightsList in the SearchResultEntry is of the form
specified in the LDIF BNF for <right>.
dnType speficies the type of subject security attribute.
Defined types are access-id, group, and role.
subjectDN is a LDAP string that defines the subject or
value of the dnType. The subjectDN may be a DN or
another string such as IPAddress (dotted-decimal string
representation) on which access control is get/set. If
the subject is an entry in the directory, then the syntax
of the LDAP string is DN. We define two well-known
subjectDNs, the strings
- public - meaning public access for all users
- this - meaning the user whose name matches the entry
being accessed
Four operations are defined:
- ACI_GRANT grants the rights specified in the
rightsList for the given subject. If an access
control list does not exist for the specified
entry/attribute, then the access control list is
created with the granted rights for the given
subject. If the access control list already exists
for the specified entry/attribute, then the access
control list is modified to grant the rights for the
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given subject.
- ACI_DENY denies the rights specified in the
rightsList for the given subject. No implementation
is implied for this operation. For example, denial
of rights may be implemented as explicit denial
(negative rights) on the access control list or
removal of rights from the access control list.
- ACI_REPLACE replaces the entire access control list
for the specified entry/attribute. If an access
control list does not exist for the specified
entry/attribute, then the access control list is
created with the granted rights for the given
subject.
- ACI_DELETE deletes the entire access control list
for the specified entry/attribute.
attrs specifies the list of attributes against which the
operation is performed. attrs can be defined using a
LDAP filter expression.
7. Access Control Information (ACI) Controls
The access control information controls provide a way to
manipulate access control information in conjunction with
an LDAP operation such as ldap_add, ldap_modify, or
ldap_search. Three LDAP controls are defined for
transmission of access control information. These
controls allow access control information to be get/set
while manipulating other directory information. The
controls are:
- getEffectiveRights to obtain the effective rights
for a given directory entry(s) for a given subject
during a ldap_search operation
- listSubjectRights to get the access control
information for a given directory entry(s) during a
ldap_search operation
- specifyCredentials to specify a set of credentials
for the bind identity (DN) during a ldap_bind
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operation
7.1 getEffectiveRights Control
7.1.1 Request Control
This control is included in the ldap_search message as
part of the controls field of the LDAPMessage, as
defined in Section 4.1.12 of [LDAPv3].
The controlType is set to <OID to be assigned>. The
criticality MAY be either TRUE or FALSE (where absent is
also equivalent to FALSE) at the client's option. The
controlValue is an OCTET STRING, whose value is the BER
encoding of a value of the following SEQUENCE:
getEffectiveRightsRequest ::= SEQUENCE {
targetDN LDAPDN,
effectiveRightsRequest SEQUENCE OF SEQUENCE {
rightsFamily LDAPOID | "*",
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
dnType LDAPOID | "*",
subjectDN LDAPString,
}
}
The targetDN specifies the initial directory entry in DN
syntax on which the getEffectiveRights control is
performed. request is a set of sequences that state the
whichObject (entry or entry plus subtree) and specifics
of the control request to be performed. One or more
rightsFamily can be be obtained for a given subjectDN ad
dnType. A "*" in the rightsFamily field indicates that
the rights for all rights families defined for the
subjectDN / dnType are to be returned. This control is
applied to the scope set by the ldap_search operation,
i.e. base, one-level, subtree.
7.1.2 Response Control
This control is included in the ldap_search_response
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message as part of the controls field of the LDAPMessage,
as defined in Section 4.1.12 of [LDAPv3].
The controlType is set to <OID to be assigned>. The
criticality MAY be either TRUE or FALSE (where absent is
also equivalent to FALSE). The controlValue is an OCTET
STRING, whose value is the BER encoding of a value of the
following SEQUENCE:
getEffectiveRightsResponse ::= {
result ENUMERATED {
success (0),
operationsError (1),
unavailableCriticalExtension (12),
noSuchAttribute (16),
undefinedAttributeType (17),
invalidAttributeSyntax (21),
unavailable (52),
unwillingToPerform (53),
other (80)
}
}
The effective rights returned are returned with each
attribute returned by the search result. So, the result
for ldap_search is:
SearchResultEntry ::= [APPLICATION 4] SEQUENCE {
objectName LDAPDN,
rightsAttributes PartialEffectiveRightsList }
PartialEffectiveRightsList ::= SEQUENCE OF SEQUENCE {
rightFamily LDAPOID,
rightsList ENUMERATED,
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
}
}
Although this extends the search operation, there are no
incompatibilities between versions. LDAPv2 cannot send a
control, hence the above structure cannot be returned to
a LDAPv2 client. A LDAPv3 client cannot send this
request to a LDAPv2 server. A LDAPv3 server not
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supporting this control cannot return the additional
data.
7.1.3 Client-Server Interaction
The getEffectiveRightsRequest control requests the rights
that MUST be in effect for requested directory
entry/attribute based on the subject DN. The server that
consumes the search operation looks up the rights for the
returned directory information based on the subject DN
and returns that rights information.
There are six possible scenarios that may occur as a
result of the getEffectiveRights control being included
on the search request:
1. If the server does not support this control and the
client specified TRUE for the control's criticality
field, then the server MUST return
unavailableCriticalExtension as a return code in
the searchResponse message and not send back any
other results. This behavior is specified in
section 4.1.12 of [LDAPv3].
2. If the server does not support this control and the
client specified FALSE for the control's
criticality field, then the server MUST ignore the
control and process the request as if it were not
present. This behavior is specified in section
4.1.12 of [LDAPv3].
3. If the server supports this control but for some
reason such as cannot process specified
rightsFamily and the client specified TRUE for the
control's criticality field, then the server SHOULD
do the following: return
unavailableCriticalExtension as a return code in
the searchResult message.
4. If the server supports this control but for some
reason such as cannot process specified
rightsFamily and the client specified FALSE for the
control's criticality field, then the server should
process as 'no rights returned for that family' and
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include the result Unavailable in the
getEffectiveRightsResponse control in the
searchResult message.
5. If the server supports this control and can return
the rights per the rightsFamily information, then
it should include the getEffectiveRightsResponse
control in the searchResult message with a result
of success.
6. If the search request failed for any other reason,
then the server SHOULD omit the
getEffectiveRightsResponse control from the
searchResult message.
The client application is assured that the correct rights
are returned for scope of the search operation if and
only if the getEffectiveRightsResponse control returns
the rights. If the server omits the
getEffectiveRightsResponse control from the searchResult
message, the client SHOULD assume that the control was
ignored by the server.
The getEffectiveRightsResponse control, if included by
the server in the searchResponse message, should have the
getEffectiveRightsResult set to either success if the
rights are returned or set to the appropriate error code
as to why the rights could not be returned.
The server may not be able to return a right because it
may not exist in that directory object's attribute; in
this case, the rights request is ignored with success.
7.2 listSubjectRights Control
7.2.1 Request Control
This control is included in the ldap_search message as
part of the controls field of the LDAPMessage, as
defined in Section 4.1.12 of [LDAPv3].
The controlType is set to <OID to be assigned>. The
criticality MAY be either TRUE or FALSE (where absent is
also equivalent to FALSE) at the client's option. The
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controlValue is an OCTET STRING, whose value is the BER
encoding of a value of the following SEQUENCE:
listSubjectRightsRequest ::= SEQUENCE {
targetDN LDAPDN,
listRightsRequest SEQUENCE OF SEQUENCE {
rightsFamily LDAPOID | "*",
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
dnType LDAPOID | "*",
listSubjectDN LDAPString | "*",
}
}
The targetDN specifies the initial directory entry in DN
syntax on which the listSubjectRights control is
performed. request is a set of sequences that state the
whichObject (entry or entry plus subtree) and specifics
of the control request to be performed. One or more
rightsFamily can be be obtained for a given subjectDN ad
dnType. A "*" in the rightsFamily field indicates that
the rights for all rights families defined for the
subjectDN / dnType are to be returned. A "*" in the
dnType field indicates that all dnTypes are processed by
this request. A "*" in the subjectDN field indicates
that all subjectDNs are processed by this request. The
scope of the operation is controlled by the scope set in
the ldap_search operation.
7.2.2 Response Control
This control is included in the ldap_search message as
part of the controls field of the LDAPMessage, as defined
in Section 4.1.12 of [LDAPv3].
The controlType is set to <OID to be assigned>. The
criticality MAY be either TRUE or FALSE (where absent is
also equivalent to FALSE). The controlValue is an OCTET
STRING, whose value is the BER encoding of a value of the
following SEQUENCE:
listSubjectRightsResponse ::= {
result ENUMERATED {
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success (0),
operationsError (1),
unavailableCriticalExtension (12),
noSuchAttribute (16),
undefinedAttributeType (17),
invalidAttributeSyntax (21),
unavailable (52),
unwillingToPerform (53),
other (80)
}
}
The subjects' rights returned are returned with each
attribute returned by the search result. So, the result
for ldap_search is:
SearchResultEntry ::= [APPLICATION 4] SEQUENCE {
objectName LDAPDN,
attributes PartialSubjRightsAttributeList }
PartialSubjRightsAttributeList ::= SEQUENCE OF SEQUENCE
{
rightFamily LDAPOID,
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
subjectDnType LDAPOID,
subjectDN LDAPString,
rightsList ENUMERATED
}
Although this extends the search operation, there are no
incompatibilities between versions. LDAPv2 cannot send a
control, hence the above structure cannot be returned to
a LDAPv2 client. A LDAPv3 client cannot send this
request to a LDAPv2 server. A LDAPv3 server not
supporting this control cannot return the additional
data.
7.2.3 Client-Server Interaction
The listSubjectRightsRequest control specifies the rights
that MUST be returned for the scope of the search. The
server that consumes the search operation looks up the
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rights for the returned directory information and returns
the result as search information associated with the
scope of that search.
There are six possible scenarios that may occur as a
result of the listSubjectRights control being included on
the search request:
1. If the server does not support this control and the
client specified TRUE for the control's criticality
field, then the server MUST return
unavailableCriticalExtension as a return code in
the searchResponse message and not send back any
other results. This behavior is specified in
section 4.1.12 of [LDAPv3].
2. If the server does not support this control and the
client specified FALSE for the control's
criticality field, then the server MUST ignore the
control and process the request as if it were not
present. This behavior is specified in section
4.1.12 of [LDAPv3].
3. If the server supports this control but for some
reason such as cannot process specified
rightsFamily and the client specified TRUE for the
control's criticality field, then the server SHOULD
do the following: return
unavailableCriticalExtension as a return code in
the searchResult message and omit the
listSubjectRightsResponse control in the
searchResult message.
4. If the server supports this control but for some
reason such as cannot process specified
rightsFamily and the client specified FALSE for the
control's criticality field, then the server should
process as 'no rights returned for that family' and
include the result Unavailable in the
listSubjectRightsResponse control in the
searchResult message.
5. If the server supports this control and can return
the rights per the rightsFamily information, then
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it should include the listSubjectRightsResponse
control in the searchResult message with a result
of success.
6. If the search request failed for any other reason,
then the server SHOULD omit the
listSubjectRightsResponse control from the
searchResult message.
The client application is assured that the correct rights
are returned for the scope of the search operation if and
only if the listSubjectRightsResponse control returns the
rights. If the server omits the
listSubjectRightsResponse control from the searchResponse
message, the client SHOULD assume that the control was
ignored by the server.
The listSubjectRightsResponse control, if included by the
server in the searchResponse message, should have the
searchResult set to either success if the rights were
returned or set to the appropriate error code as to why
the rights could not be returned.
The server may not be able to return a right because it
may not exist in that directory object's attribute; in
this case, the rights request is ignored with success.
7.3 specifyCredentials Control
7.3.1 Request Control
This control is included in the ldap_bind message as
part of the controls field of the LDAPMessage, as
defined in Section 4.1.12 of [LDAPv3].
The controlType is set to <OID to be assigned>. The
criticality MAY be either TRUE or FALSE (where absent is
also equivalent to FALSE) at the client's option. The
controlValue is an OCTET STRING, whose value is the BER
encoding of a value of the following SEQUENCE:
specifyCredentialRequest ::= SEQUENCE {
credential LDAPString
}
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}
The credential specifies the credential (e.g. groups,
roles, etc) that the client is requesting be associated
with the bind DN for access control determination in
subsequent ldap operations. This provides a 'push' model
for credentials where the client attempts to 'push' the
credential to the server. The server may process at bind
time as follows:
- server may unconditionally ignore
- server may unconditionally accept
- server may define trust model and evaluate of the
trust of each credential
If this control is not used, it is assumed that the
server determines (pulls) the credentials associated with
the bind DN when needed in subsequent ldap operations to
provide access control.
7.3.2 Response Control
This control is included in the ldap_search message as
part of the controls field of the LDAPMessage, as defined
in Section 4.1.12 of [LDAPv3].
The controlType is set to <OID to be assigned>. The
criticality MAY be either TRUE or FALSE (where absent is
also equivalent to FALSE). The controlValue is an OCTET
STRING, whose value is the BER encoding of a value of the
following SEQUENCE:
specifyCredentialsResponse ::= {
result ENUMERATED {
success (0),
operationsError (1),
unavailableCriticalExtension (12),
unavailable (52),
unwillingToPerform (53),
other (80)
}
}
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No data is returned; just the result is returned.
Although this extends the bind operation, there are no
incompatibilities between versions. LDAPv2 cannot send a
control. A LDAPv3 client cannot send this request to a
LDAPv2 server. A LDAPv3 server not supporting this
control cannot return the additional data.
7.3.3 Client-Server Interaction
The specifyCredentialsRequest control specifies the
credentials that the client was the server to use for
access control in subsequent ldap operations. The server
that consumes the bind operation may unconditionally
accept, ignore, or evaluate the trust of the specified
credentials at bind time and returns only a success or
failure response (no data returned).
There are six possible scenarios that may occur as a
result of the specifyCredential control being included on
the bind request:
1. If the server does not support this control and the
client specified TRUE for the control's criticality
field, then the server MUST return
unavailableCriticalExtension as a return code in
the bindResponse message. This behavior is
specified in section 4.1.12 of [LDAPv3].
2. If the server does not support this control and the
client specified FALSE for the control's
criticality field, then the server MUST ignore the
control and process the request as if it were not
present. This behavior is specified in section
4.1.12 of [LDAPv3].
3. If the server supports this control but for some
reason such as cannot process specified credential
(e.g. server decided to evaluate the trust of that
credential and the result is the server not
trusting all the credentials or unconditionally
ignores the credential) and the client specified
TRUE for the control's criticality field, then the
server SHOULD do the following: return
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unavailableCriticalExtension as a return code in
the bindResult message and omit the
specifyCredentialResponse control in the bindResult
message.
4. If the server supports this control but for some
reason such as cannot process specified credential
(e.g. server decided to evaluate the trust of that
credential and the result is the server not
trusting all the credentials or unconditionally
ignores the credential) and the client specified
FALSE for the control's criticality field, then the
server should process as 'credential ignored' and
include the result Unavailable in the
specifyCredentialResponse control in the bindResult
message.
5. If the server supports this control and evaulates
the trust of that credential and the result is the
server trusting all the credentials, then it should
include the specifyCredentialResponse control in
the bindResult message with a result of success.
6. If the bind request failed for any other reason,
then the server SHOULD omit the
specifyCredentialResponse control from the
bindResult message.
The client application is assured that the correct
credentials are used by the server when specified by the
client for subsequent ldap operations if and only if the
specifyCredentialResponse is successful. If the server
omits the specifyCredentialResponse control from the
searchResponse message, the client SHOULD assume that the
control was ignored by the server.
The specifyCredentialResponse control, if included by the
server in the bindResponse message, should have the
bindResult set to either success if the credentials were
accepted by the server or set to the appropriate error
code as to why the credentials were not accepted.
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8. Access Control Extended Operations
Two extended operations (analogous to the controls) are
defined for transmission of access control information.
These operations help with the management of access
control information independent of manipulating other
directory information. The extended operations are:
- LDAP Get Effective Rights to obtain the effective
rights for a given directory entry for a given
subject
- LDAP List Subject Rights to get the access control
information for a given directory entry
8.1 LDAP Get Effective Rights Operation
ldapGetEffectiveRightsRequest ::= [APPLICATION 23]
SEQUENCE {
requestName [0] <OID to be assigned>,
requestValue [1] OCTET STRING OPTIONAL }
where
requestValue ::= SEQUENCE {
targetDN LDAPDN,
updates SEQUENCE OF SEQUENCE {
rightsFamily LDAPOID | "*",
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
dnType LDAPOID | "*",
subjectDN LDAPString,
}
}
The requestName is a dotted-decimal representation of the
OBJECT IDENTIFIER corresponding to the request. The
requestValue is information in a form defined by that
request, encapsulated inside an OCTET STRING.
The server will respond to this with an LDAPMessage
containing the ExtendedResponse which is a rights list.
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ldpGetEffectiveRightsResponse ::= [APPLICATION 24]
SEQUENCE {
COMPONENTS OF LDAPResult,
responseName [10] <OID to be assigned> OPTIONAL,
effectiveRights [11] OCTET STRING OPTIONAL }
where
effectiveRights ::= SEQUENCE OF SEQUENCE {
rightFamily LDAPOID,
rightsList ENUMERATED,
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
subjectDnType LDAPOID,
subjectDN LDAPSTRING
}
If the server does not recognize the request name, it
MUST return only the response fields from LDAPResult,
containing the protocolError result code.
8.2 LDAP List Subject Rights
ldapListSubjectRightsRequest ::= [APPLICATION 23]
SEQUENCE {
requestName [0] <OID to be assigned>,
requestValue [1] OCTET STRING }
where
requestValue ::= SEQUENCE {
targetDN LDAPDN,
updates SEQUENCE OF SEQUENCE {
rightsFamily LDAPOID | "*",
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
dnType LDAPOID | "*",
listSubjectDN LDAPString | "*",
}
}
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The requestName is a dotted-decimal representation of the
OBJECT IDENTIFIER corresponding to the request. The
requestValue is information in a form defined by that
request, encapsulated inside an OCTET STRING.
The server will respond to this with an LDAPMessage
containing the ExtendedResponse which is a result code.
ldapListSubjectRightsResponse ::= [APPLICATION 24]
SEQUENCE {
COMPONENTS OF LDAPResult,
responseName [10] <OID to be assigned> OPTIONAL,
subjectRightsList [11] OCTET STRING OPTIONAL }
where
subjectRightsList ::= SEQUENCE OF SEQUENCE {
rightFamily LDAPOID,
whichObject ENUMERATED {
LDAP_ENTRY (1),
LDAP_SUBTREE (2)
},
subjectDnType LDAPOID,
subjectDN LDAPString,
perms SEQUENCE OF SEQUENCE {
rightsList ENUMERATED,
attrs LDAPSTRING
}
}
}
If the server does not recognize the request name, it
MUST return only the response fields from LDAPResult,
containing the protocolError result code.
9. Operational Semantics of Access Control Operations
The semantics of access control operations described in
this document are defined operationally in terms of
"histories". A history is a sequence of actions (x1, x2,
..., xN).
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We consider five types of actions:
- LDAP Access Control Policy Update actions:
invocations of the LDAP Update Access Extended
Operation or LDAP Update Access Control.
- LDAP Access Control Policy Query operations:
invocations of the LDAP Get Effective Access
Extended Operation, LDAP Get Effective Access
Control, LDAP List Subject Rights Extended
Operation, or LDAP List Subject Rights Control.
- Datastore Access Control Policy Update Actions: any
operation implemented by the server which LDAP is
using as its datastore which changes the access
policy enforced with respect to attempts to access
LDAP directory entries and their attributes.
- LDAP Access Request operations: invocations of LDAP
entry or attribute access operations (Read, Update,
Search, Compare, etc...).
- Other operations: anything else, including Datastore
operations which do not change the access policy
enforced by the server.
The semantics of histories are defined as follows:
- LDAP Update (Replace), LDAP Query
The Query will show that the subject has all rights
granted by the Update operation, and no rights not
granted by the Update operation.
- LDAP Update (Grant), LDAP Query
The Query will show that the subject has all rights
granted by the Update operation. The Query may show
that the subject also has other rights not granted
by the Update operation, depending on the policy in
force before the Update operation.
- LDAP Update (Deny), LDAP Query
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The Query will show that the subject does not have
any right denied by the Update operation. The Query
may show that the subject has rights not denied by
the Update operation, depending on the policy in
force before the Update operation.
- LDAP Update (Replace), LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request will fail with an access-
denied exception if it requires any right not
granted by the Update operation.
- LDAP Update (Grant), LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request may succeed if it requires
rights not granted by the Update operation,
depending on the policy in force before the Update
operation.
- LDAP Update (Deny), LDAP Access Request
The Request will fail with an access-denied
exception if it requires any right denied to the
requesting subject by the Update operation. If the
Request requires only rights which were not denied
by the Update operation, it may succeed, depending
on the policy in force before the Update operation.
- LDAP Update (Replace), Other, LDAP Query
The Query will show that the subject has all rights
granted by the Update operation, and no rights not
granted by the Update operation.
- LDAP Update (Grant), Other, LDAP Query
The Query will show that the subject has all rights
granted by the Update operation. The Query may show
that the subject also has other rights not granted
by the Update operation, depending on the policy in
force before the Update operation.
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- LDAP Update (Deny), Other, LDAP Query
The Query will show that the subject does not have
any right denied by the Update operation. The Query
may show that the subject has rights not denied by
the Update operation, depending on the policy in
force before the Update operation.
- LDAP Update (Replace), Other, LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request will fail with an access-
denied exception if it requires any right not
granted by the Update operation.
- LDAP Update (Grant), Other, LDAP Access Request
The Request will succeed if it requires only rights
granted to the requesting subject by the Update
operation. The Request may succeed if it requires
rights not granted by the Update operation,
depending on the policy in force before the Update
operation.
- LDAP Update (Deny), Other, LDAP Access Request
The Request will fail with an access-denied
exception if it requires any right denied to the
requesting subject by the Update operation. If the
Request requires only rights which were not denied
by the Update operation, it may succeed, depending
on the policy in force before the Update operation.
- LDAP Update (Replace), Datastore Update, LDAP Query
The result of the Query is not defined.
- LDAP Update (Grant), Datastore Update, LDAP Query
The result of the Query is not defined.
- LDAP Update (Deny), Datastore Update, LDAP Query
The result of the Query is not defined.
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- LDAP Update (Replace), Datastore Update, LDAP Access
Request
The result of the Access Request is not defined.
- LDAP Update (Grant), Datastore Update, LDAP Access
Request
The result of the Access Request is not defined.
- LDAP Update (Deny), Datastore Update, LDAP Access
Request
The result of the Access Request is not defined.
10. LDIF Syntax for Access Control Information
10.1 LDIF Purpose
The intent of the LDIF is to design a common interchange
format. Any given LDAP server should be able to translate
the below defined LDIF into a meaningful request. Each
server should be able to understand each part of the
LDIF; there should not be any ambiguity into what any
part of the syntax means.
While the end goal is to have a common behavior model
between different LDAP server implementations, the LDIF
alone will not ensure identical ACL processing behavior
between servers. The semantics of how a server
interprets the aci syntax are not defined here. What
'deny' means on server1 might be different than on
server2.
The LDIF maintains an assumption that the receiving
server supports inheritance within the security model. If
the server does not support inheritance, the receiving
server must expand any inherited information based on the
scope flag.
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10.2 ACL Attributes
There are three attributes which are allowed on all
directory objects: aci, vendorAci and policyOwner. The
syntax of these attributes is defined below. The aci,
vendorAci and policyOwner attribute are all multivalued.
In determining the order of the syntax, the DN was left
until the end for parsing reasons. Examples follow the
BNF
10.2.1 VendorACI_
The Vendor specific ACI information is listed in its own
attribute. The assumption here is that if the vendor's
need to provide information in an additional attribute,
then the vendor specific information would not
necessarily be of the same syntax as the ACI attribute
which would have < acl syntax> .
10.2.2 Policy Owner_
The intent behind policy ownership is that it controls
administrative subdomains. It can also control who has
permission to set / change acls for implementations that
do not have an acl controlling access to itself. If
there are multiple policy owners it is implementation
specific as to the behavior of whether policy owner #1
can override policy owner # 2.
The syntax for policyOwner includes the 'scope' flag.
Servers which do not support inheritance must expand the
policyOwner inheritance similar to the expansion of the
ACI. If the policy owner is not specified for any
object in the tree, behavior is implementation defined.
For instance, if no object anywhere in the tree has a
policy owner, then the server could simply assert that
the 'root DN' is considered the policy owner for all
objects. An alternate approach might be that the
implementation defines the entryDN to be the policy
owner.
The policyOwner and ACI are left as distinct attributes
for several reasons. They syntax of the policy owner is
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very similar to the syntax of the ACI. In parsing, it
would be difficult to tell when one stops and the other
begins (especially since there are no reserved characters
in LDAP Dns ). Additionally, the inheritance models of
the administrative subdomains may be different then the
models guiding the ACI inheritance. Since there is no
flag to tell if a given ACI is explicit vs inherited,
combining the two sets of information ties the
policyOwner inheritance to ACI inheritance. Additionally,
keeping the information separate makes it easier for the
applications to construct views of various models by only
requesting the information they need.
10.2.3 ACI
The aci attribute is defined using < acl syntax>. Within
the acl syntax, the family OID describes the permissions,
dnType, subhectDn and scope that will be found in the
following string. The permissions for the IETF family
are found below. The family OID is listed first in the
syntax to be consistent with other LDAP LDIF definitions
which list OIDs first. If the OID within the ACI
attribute is listed as other than the IETF family oid,
the syntax is the same as l isted below, but one or more
of the scope, dnType, subjectDn or permissions may vary
from the IETF defined syntax.
Within the acl syntax, there is a string which describes
the rights. This is a composite of the permissions and
resources to which the user is being granted or denied
access. The set of permissions is fixed. Either of the
actions "grant" | "deny" may be used when creating or
updating an aci.
Using the BNF defined below, it is possible for the
permission string to be empty. The aci
aci:
1.2.3.4#subtree#grant;;attribute1$grant;r,s;[all]#group#cn=Dept
XYZ, c=US
mean that this group is granted permission to read and
search all attributes except attribute1.
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Similarly, the aci
aci: 1.2.3.4#subtree#group#cn=Dept XYZ, c=US simply
means that no permissions have been defined for this
group. It is up to the server implementation as to
whether the group does or does not receive permission to
attributes on an entry with an empty rights list.
The attributeString is an attribute Name (defined to be a
printable string). If the string refers to an attribute
not defined in the given server's schema, the server
SHOULD report an error. Another option for the
attributeString is "[entry]". This is provided to
describe permissions which apply to an entire object.
This could mean actions such as delete the object, or add
a child object. The third option for attributeString is
"[all]" which means the permission set should apply to
all attributes.
If the keyword "[all]" and another attribute are both
specified within an aci, the more specific permission set
for the attribute overrides the less specific permission
set for "[all]". If two acis contain identical
familyOID, scope, DnTypes and DNs, the permission given
DN is specified in two distinct acis on any given entry,
the rights lists can be combined into one list. For
example:
aci: 1.2.3.4#subtree#group#grant;r,w;[all]#cn=Dept XYZ
aci: 1.2.3.4#subtree#group#grant;r;attribute1#cn=Dept
XYZ
is the equivalent of
aci:
1.2.3.4#subtree#group#grant;r,w;[all];r,attribute1#cn=Dept
XYZ
Multiple attributeStrings can be listed after any given
permission set; for instance, "r,w ; attribute1,
attribute2". This means that if the server supports a
attribute aggregation mechanism, attribute1 and
attribute2 should be considered to be part of the same
group. If the server does not support a grouping
mechanism, the permission set applies independently to
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attribute1 and attribute2. For servers that do not
support attribute grouping, "r,w ; attribute1,
attribute2" results in the same operations as " r,w;
attribute1; r,w; attribute2 "
Within the vendorACI, the oid determines the format or
the printable string to follow.
10.3 Modifying the ACI Values
The attribute: value pairs listed below would be possible
inputs for normal LDAP operations such as ldapadd and
ldapmodify. Within the ldapmodify command there are
three changetypes: add, delete, replace.
Replace works similarly to all other attributes. If the
attribute value does not exist, create the value. If the
attribute does exist, replace the value. If the aci
value is replaced, all aci values are replaced. Given an
aci for an entry:
aci:
1.2.3.4#subtree#deny;r,w;[all];grant;rsc;attirbute2#group#cn=Dept
ABC
aci:
1.2.3.4#subtree#grant;r,;[all];grant;rsc;attirbute1#group#cn=Dept
XYZ
perform the following change:
dn: cn=someEntry
changetype: replace
add: aci
aci: 1.2.3.4#subtree#grant;r,w;[all];#group#cn=Dept LMN
The resulting acl is:
aci: 1.2.3.4#subtree#grant;r,w;[all];#group#cn=Dept LMN
(aci values for Dept XYZ and ABC are lost through the
replace)
During an ldapmodify-add, if the aci does not exist, the
create the aci with the specific aci value(s). If the
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aci does exist, then add the specified values to the
given aci. For example a given aci:
aci: 1.2.3.4#subtree#group#grant;r,w;[all]#cn=Dept XYZ
with a modification:
dn: cn=someEntry
changetype: add
add: aci
aci: 1.2.3.4#subtree#group#grant;r;attribute1#cn=Dept
XYZ
would yield an aci value of:
aci:
1.2.3.4#subtree#group#grant;r,w;[all];r,attribute1#cn=Dept
XYZ
To delete an entire acl, use ldapmodify - delete without
specifying a value for the aci. The entry would then
inherit its aci from some other node in the tree
depending on the server inheritance model.
dn: cn = some Entry
changetype: delete
delete: aci
During an ldapmodify-delete, there are two possible
interpretations of the delete.
dn: cn = some Entry
changetype: delete
delete: aci
aci: < > (see below)
Interpretation 1.
aci: 1.2.3.4#subtree#group#cn=Dept XYZ
would delete the entire aci for the group cn=Dept XYZ
Interpretation 2.
aci:
1.2.3.4#subtree#grant;rsc;attribute1#group#cn=Dept XYZ
would delete the 'grant;rsc;attribute1' portion of the
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aci
for the group cn=Dept XYZ
before ldapmodify - delete:
aci:
1.2.3.4#subtree#group#grant;r,w;[all];grant;rsc;attribute1#cn=Dept
XYZ
after ldapmodify - delete of attribute1
aci: 1.2.3.4#subtree#group#grant;r,w;[all];#cn=Dept
XYZ
if the delete is for an attribute not existing within
the aci, nothing
is changed in the expected outcome. For example, if now
attribute2
is deleted,
aci: 1.2.3.4#subtree#grant;[attribute2]#group#cn=Dept
XYZ
the resulting aci would still be
aci: 1.2.3.4#subtree#group#grant;r,w;[all];#cn=Dept
XYZ
10.4 BNF
<aci> ::= <acl syntax>
<vendorAci > ::= <oid> + '#' + <printable string>
<acl syntax> ::= <familyOID> + '#' + <scope> + '#' +
<rights> + '#' + <dnType> + '#' + <subjectDn>
<policyOwner> ::= <familyOid> + '#' + <scope> + '#' +
<dnType> + '#' + <subjectDn>
<subjectDn> ::= <printable string>
<familyOid> ::= < oid >
<scope> :: "entry" | "subtree"
<dnType> :: "access-id" | "role" | "group"
<rights> ::= [ ] | [ < right > + [ '$' + <right> ] * ]
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<right> ::= <action> + ';' + <permissions> +
';' + <attrs>
<action> ::= "grant" | "deny"
<permissions> ::= [ ] | [ < permission > +
[ ',' + <permission> ] * ]
<attrs > ::= [ <attributeString> +
[ ',' + <attributeString > ] * ]
<attributeString> ::= "[all]" | "[entry]" |
<printableString>
<permission> : "a" | "d" | "r" | "s" | "w" | "c"
| "g" | "s" | "m" | "u"
These are the permissions defined for
the IETF family OID.
10.5 Examples
Suppose IETFFamilyOID = 1.2.3.4
The following two examples show an administrative
subdomain being established. The first example shows a
single user being assigned the policyOwner for the entire
domain. The second example shows a group of ids assigned
to the policy Owner.
policyOwner: 1.2.3.4#subtree#access-id#cn=Hoyt
policyOwner: 1.2.3.4#subtree#group#cn=System Owners,
o=Company
The next example shows an aci attribute where a group
"cn=Dept XYZ, c=US" is being given permissions to read,
search and compare attribute1. The permission should
apply to the entire subtree below the node containing
this aci.
aci: 1.2.3.4#subtree#group#grant;r,s,c;attribute1#cn=Dept
XYZ, c=US
The next example shows an ACI attribute where a role
"cn=SysAdmins,o=Company" is being given permissions to
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add objects below this node, and read, search and compare
attributes2 and 3. The permission should apply to the
entire subtree below the node containing this ACI.
aci:
1.2.3.4#subtree#role#grant;a;[entry]$grant;r,s,c;attribute2,attribute3#cn=SysAdmins,o=Company
11. Security Considerations
This draft proposes protocol elements for transmission of
security policy information. Security considerations are
discussed throughout this draft. Because subject
security attribute information is used to evaluate
decision requests, it is security-sensitive information
and must be protected against unauthorized modification
whenever it is stored or transmitted.
12. References
[LDAPv3] M. Wahl, T. Howes, S. Kille, "Lightweight
Directory Access Protocol (v3)", RFC 2251, December 1997.
[ECMA] ECMA, "Security in Open Systems: A Security
Framework" ECMA TR/46, July 1988
[REQTS] Stokes, Byrne, Blakley, "Access Control
Requirements for LDAP, INTERNET-DRAFT <draft-ietf-
ldapext-acl-reqts-01.txt>, August 1998.
[ATTR] M.Wahl, A, Coulbeck, T. Howes, S. Kille,
"Lightweight Directory Access Protocol (v3)": Attribute
Syntax Definitions, RFC 2252, December 1997.
[UTF] M. Wahl, S. Kille, "Lightweight Directory Access
Protocol (v3)": A UTF-8 String Representation of
Distinguished Names", RFC 2253, December 1997.
[Bradner97] Bradner, Scott, "Key Words for use in RFCs to
Indicate Requirement Levels", RFC 2119.
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AUTHOR(S) ADDRESS
Ellen Stokes Bob Blakley
IBM Dascom
11400 Burnet Rd
Austin, TX 78758 Austin, TX
USA USA
mail-to: stokes@austin.ibm.com mail-to: blakley@dascom.com
phone: +1 512 838 3725
fax: +1 512 838 8597
Debbie Byrne
IBM
11400 Burnet Rd
Austin, TX 78758
USA
mail-to: djbyrne@us.ibm.com
phone: +1 512 838 1960
fax: +1 512 838 0156
Stokes, Byrne, Blakley Expires 15 October 1999 [Page 39]
Internet-Draft Access Control Model 15 April 1999
Stokes, Byrne, Blakley Expires 15 October 1999 [Page 40]
CONTENTS
1. Introduction....................................... 2
2. Overview........................................... 2
3. Terminology........................................ 3
4. The Model.......................................... 6
4.1 Access Control Activity Lifecycle............ 6
4.2 Access Control Information Model............. 6
4.3 Bind and Credentials......................... 8
5. Access Control Information Schema.................. 8
5.1 Attributes................................... 8
5.1.1 Root DSE Attribute for Access
Control Mechanism 8
5.1.2 Subschema Attribute for Access
Control Mechanism 9
5.2 Other Defined Parameters/OIDs................ 9
5.2.1 Rights Families and Rights 9
5.2.2 DN Types 10
6. Access Control Parameters for LDAP Controls &
Extended Operations................................ 10
7. Access Control Information (ACI) Controls.......... 12
7.1 getEffectiveRights Control................... 13
7.1.1 Request Control 13
7.1.2 Response Control 13
7.1.3 Client-Server Interaction 15
7.2 listSubjectRights Control.................... 16
7.2.1 Request Control 16
7.2.2 Response Control 17
7.2.3 Client-Server Interaction 18
7.3 specifyCredentials Control................... 20
7.3.1 Request Control 20
7.3.2 Response Control 21
7.3.3 Client-Server Interaction 22
8. Access Control Extended Operations................. 24
8.1 LDAP Get Effective Rights Operation.......... 24
8.2 LDAP List Subject Rights..................... 25
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9. Operational Semantics of Access Control
Operations......................................... 26
10. LDIF Syntax for Access Control Information......... 30
10.1 LDIF Purpose................................. 30
10.2 ACL Attributes............................... 31
10.2.1 VendorACI 31
10.2.2 Policy Owner 31
10.2.3 ACI 32
10.3 Modifying the ACI Values..................... 34
10.4 BNF.......................................... 36
10.5 Examples..................................... 37
11. Security Considerations............................ 38
12. References......................................... 38
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