Request for Comments: 4532
Category: Standards Track
Lightweight Directory Access Protocol (LDAP)
"Who am I?" Operation
Status of This Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright © The Internet Society (2006).
This specification provides a mechanism for Lightweight Directory Access Protocol (LDAP) clients to obtain the authorization identity the server has associated with the user or application entity. This mechanism is specified as an LDAP extended operation called the LDAP "Who am I?" operation.
1. Background and Intent of Use
This specification describes a Lightweight Directory Access Protocol (LDAP) [RFC4510] operation that clients can use to obtain the primary authorization identity, in its primary form, that the server has associated with the user or application entity. The operation is called the "Who am I?" operation.
This specification is intended to replace the existing Authorization Identity Controls [RFC3829] mechanism, which uses Bind request and response controls to request and return the authorization identity. Bind controls are not protected by security layers established by the Bind operation that includes them. While it is possible to establish security layers using StartTLS [RFC4511][RFC4513] prior to the Bind operation, it is often desirable to use security layers established by the Bind operation. An extended operation sent after a Bind operation is protected by the security layers established by the Bind operation.
There are other cases where it is desirable to request the authorization identity that the server associated with the client separately from the Bind operation. For example, the "Who am I?" operation can be augmented with a Proxied Authorization Control [RFC4370] to determine the authorization identity that the server associates with the identity asserted in the Proxied Authorization Control. The "Who am I?" operation can also be used prior to the Bind operation.
Servers often associate multiple authorization identities with the client, and each authorization identity may be represented by multiple authzId [RFC4513] strings. This operation requests and returns the authzId that the server considers primary. In the specification, the term "the authorization identity" and "the authzId" are generally to be read as "the primary authorization identity" and the "the primary authzId", respectively.
1.1. Conventions Used in This Document
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 BCP 14 [RFC2119].
2. The "Who am I?" Operation
The "Who am I?" operation is defined as an LDAP Extended Operation [RFC4511] identified by the whoamiOID Object Identifier (OID). This section details the syntax of the operation's whoami request and response messages.
whoamiOID ::= "126.96.36.199.4.1.4188.8.131.52"
2.1. The whoami Request
The whoami request is an ExtendedRequest with a requestName field containing the whoamiOID OID and an absent requestValue field. For example, a whoami request could be encoded as the sequence of octets (in hex):
30 1e 02 01 02 77 19 80 17 31 2e 33 2e 36 2e 31 2e 34 2e 31 2e 34 32 30 33 2e 31 2e 31 31 2e 33
2.2. The whoami Response
The whoami response is an ExtendedResponse where the responseName field is absent and the response field, if present, is empty or an authzId [RFC4513]. For example, a whoami response returning the authzId "u:xxyyz@EXAMPLE.NET" (in response to the example request) would be encoded as the sequence of octets (in hex):
30 21 02 01 02 78 1c 0a 01 00 04 00 04 00 8b 13 75 3a 78 78 79 79 7a 40 45 58 41 4d 50 4c 45 2e 4e 45 54
3. Operational Semantics
The "Who am I?" operation provides a mechanism, a whoami Request, for the client to request that the server return the authorization identity it currently associates with the client. It also provides a mechanism, a whoami Response, for the server to respond to that request.
Servers indicate their support for this extended operation by providing a whoamiOID object identifier as a value of the 'supportedExtension' attribute type in their root DSE. The server SHOULD advertise this extension only when the client is willing and able to perform this operation.
If the server is willing and able to provide the authorization identity it associates with the client, the server SHALL return a whoami Response with a success resultCode. If the server is treating the client as an anonymous entity, the response field is present but empty. Otherwise, the server provides the authzId [RFC4513] representing the authorization identity it currently associates with the client in the response field.
If the server is unwilling or unable to provide the authorization identity it associates with the client, the server SHALL return a whoami Response with an appropriate non-success resultCode (such as operationsError, protocolError, confidentialityRequired, insufficientAccessRights, busy, unavailable, unwillingToPerform, or other) and an absent response field.
As described in [RFC4511] and [RFC4513], an LDAP session has an "anonymous" association until the client has been successfully authenticated using the Bind operation. Clients MUST NOT invoke the "Who am I?" operation while any Bind operation is in progress, including between two Bind requests made as part of a multi-stage
Bind operation. Where a whoami Request is received in violation of this absolute prohibition, the server should return a whoami Response with an operationsError resultCode.
4. Extending the "Who am I?" Operation with Controls
Future specifications may extend the "Who am I?" operation using the control mechanism [RFC4511]. When extended by controls, the "Who am I?" operation requests and returns the authorization identity the server associates with the client in a particular context indicated by the controls.
4.1. Proxied Authorization Control
The Proxied Authorization Control [RFC4370] is used by clients to request that the operation it is attached to operate under the authorization of an assumed identity. The client provides the identity to assume in the Proxied Authorization request control. If the client is authorized to assume the requested identity, the server executes the operation as if the requested identity had issued the operation.
As servers often map the asserted authzId to another identity [RFC4513], it is desirable to request that the server provide the authzId it associates with the assumed identity.
When a Proxied Authorization Control is be attached to the "Who am I?" operation, the operation requests the return of the authzId the server associates with the identity asserted in the Proxied Authorization Control. The authorizationDenied (123) result code is used to indicate that the server does not allow the client to assume the asserted identity.
5. Security Considerations
Identities associated with users may be sensitive information. When they are, security layers [RFC4511][RFC4513] should be established to protect this information. This mechanism is specifically designed to allow security layers established by a Bind operation to protect the integrity and/or confidentiality of the authorization identity.
Servers may place access control or other restrictions upon the use of this operation. As stated in Section 3, the server SHOULD advertise this extension when it is willing and able to perform the operation.
As with any other extended operations, general LDAP security considerations [RFC4510] apply.
6. IANA Considerations
The OID 184.108.40.206.4.1.4220.127.116.11 is used to identify the LDAP "Who am I?" extended operation. This OID was assigned [ASSIGN] by the OpenLDAP Foundation, under its IANA-assigned private enterprise allocation [PRIVATE], for use in this specification.
Registration of this protocol mechanism [RFC4520] has been completed by the IANA.
Subject: Request for LDAP Protocol Mechanism Registration Object Identifier: 18.104.22.168.4.1.422.214.171.124 Description: Who am I? Person & email address to contact for further information: Kurt Zeilenga <firstname.lastname@example.org> Usage: Extended Operation Specification: RFC 4532 Author/Change Controller: IESG Comments: none
This document borrows from prior work in this area, including "Authentication Response Control" [RFC3829] by Rob Weltman, Mark Smith, and Mark Wahl.
The LDAP "Who am I?" operation takes it's name from the UNIX whoami(1) command. The whoami(1) command displays the effective user ID.
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4370] Weltman, R., "Lightweight Directory Access Protocol (LDAP) Proxied Authorization Control", RFC 4370, February 2006. [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. [RFC4513] Harrison, R., Ed., "Lightweight Directory Access Protocol (LDAP): Authentication Methods and Security Mechanisms", RFC 4513, June 2006.
8.2. Informative References
[RFC3829] Weltman, R., Smith, M., and M. Wahl, "Lightweight Directory Access Protocol (LDAP) Authorization Identity Request and Response Controls", RFC 3829, July 2004. [RFC4520] Zeilenga, K., "Internet Assigned Numbers Authority (IANA) Considerations for the Lightweight Directory Access Protocol (LDAP)", BCP 64, RFC 4520, June 2006. [ASSIGN] OpenLDAP Foundation, "OpenLDAP OID Delegations", http://www.openldap.org/foundation/oid-delegate.txt.
[PRIVATE] IANA, "Private Enterprise Numbers",
Kurt D. Zeilenga
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