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Internet Engineering Task Force                                 W. Brown
Internet-Draft                              Red Hat Asia-Pacific Pty Ltd
Intended status: Standards Track                           S. Sorce, Ed.
Expires: August 31, 2017                                   Red Hat, Inc.
                                                         K. Andrews, Ed.
                                              The University of Adelaide
                                                       February 27, 2017


               Draft LDAP Single Sign On Token Processing
                     draft-wibrown-ldapssotoken-02

Abstract

   LDAP Single Sign On Token is a SASL (Simple Authentication and
   Security Layer RFC 2222 [RFC2222]) mechanism to allow single sign-on
   to an LDAP Directory Server environment.  Tokens generated by the
   LDAP server can be transmitted through other protocols and channels,
   allowing a broad range of clients and middleware to take advantage of
   single sign-on in environments where Kerberos v5 or other Single Sign
   On mechanisms may not be avaliable.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on August 31, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Format  . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  SASL Component  . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Token formats . . . . . . . . . . . . . . . . . . . . . .   3
     4.2.  SASL Client . . . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  SASL Authentication . . . . . . . . . . . . . . . . . . .   6
     4.4.  Valid Not Before Attribute  . . . . . . . . . . . . . . .   7
   5.  LDAP Component  . . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  Token Generation  . . . . . . . . . . . . . . . . . . . .   7
       5.1.1.  Token Generation Extended Operation . . . . . . . . .   8
     5.2.  Token Revocation  . . . . . . . . . . . . . . . . . . . .   8
       5.2.1.  Token Revocation Extended Operation . . . . . . . . .   9
     5.3.  Binding . . . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   7.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The need for new, simple single sign-on capable systems has arisen
   with the development of new technologies and systems.  For these
   systems we should be able to provide a simple, localised and complete
   single sign-on service.  This does not aim to replace Kerberos V5.
   It is designed for when Kerberos is too invasive for installation in
   an environment.

   Tokens generated by this system should be able to be transmitted over
   different protocols allowing middleware to relay tokens to clients.
   Clients can then contact the middleware natively and the middleware
   can negotiate the client authentication with the LDAP server.

   This implementation will provide an LDAP extended operation to create
   tokens which a client may cache, or relay to a further client.  The
   token can then be sent in a SASL bind request to the LDAP server.
   The token remains valid over many binds.  Finally, Tokens for a
   client are always able to be revoked at the LDAP Server using an LDAP



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   extended operation, allowing global logout by the user or
   administrator.

2.  Requirements Language

   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 RFC 2119 [RFC2119].

3.  Format

   This document has two components.  A SASL Mechanism, and LDAP
   extended operations.

   There is no strict requirement for the two to coexist: The LDAP
   Operation is an implementation of the service providing tokens, and
   the SASL Mechanism to authenticate them.

   In theory, an alternate protocol and database could generate and
   authenticate these tokens.

4.  SASL Component

4.1.  Token formats

   Token formats are server implementation specific: As they are the
   only entity that will decrypt and consume them, they have the option
   to provide these in any format they wish.

   This means the client will only see an opaque data structure, and
   will only need to transmit this opaque structure as part of the
   authentication request.

   For the token system to operate correctly the server MUST generate
   tokens that contain at least these three values:

   o  Date Time Issued

   o  Date Time Until

   o  User Unique Id

   As the client does not ever see the contents the User Unique Id can
   be anything within the database that uniquely identifies the user
   that is the holder of the token.

   The User Unique Id MUST be an UTF8 String.




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   The token format MUST be encrypted.  The token format can be
   decrypted with either a asymmetric or symmetric keying system.

   The token format MUST have a form of data authentication.  This can
   be through authenticated encryption, or validation of a hash.

   The Date Time Issued MUST be a complete timestamp in UTC, to prevent
   issues with changing timezones.

   Without these guarantees, the token system is not secure, and is
   vulnerable to credential forgery attacks.

   Here is an EXAMPLE ASN.1 format that would be encrypted and sent to
   the client:

   LDAPSSOToken ::= SEQUENCE {
       DateTimeIssued GeneralizedTime,
       DateTimeUntil  GeneralizedTime,
       UserUniqueId   UTF8String }

                                 Figure 1

   This would be encrypted with AES-GCM and transmitted to the client.

   Another example would be to use a fernet token Fernet Specification
   [FERNETSPEC].

   Version || Timestamp || IV || Ciphertext || HMAC

                                 Figure 2

   Timestamp can be considered to be the DateTimeIssued as:

   "This field is a 64-bit unsigned big-endian integer.  It records the
   number of seconds elapsed between January 1, 1970 UTC and the time
   the token was created."

   We can then create a Cipher text containing:

   Date Time Until || User Unique Id

                                 Figure 3

   The Date Time Until is a 64-bit unsigned big-endian integer.  It is,
   like Date Time Issued, the number of seconds since January 1, 1970
   UTC, and the token creation time added to the number of seconds of
   the requested life time.




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   This example format satisfies all of our data requirements for the
   sso token system.

4.2.  SASL Client

   The client will request a token from the authentication server.  The
   acquisition method for the token is discussed in section XXX.

   For authentication, the client MUST send the token as it was
   received.  IE changes to formatting are not permitted.

   The client MUST send the an appropriate authid in RFC 2078 [RFC2078]
   form.  This authid MUST internally match the User Unique Id in the
   token.  The server is responsible for this validation.

   The client MAY transform the token if acting in a proxy fashion.
   However this transformation must be deterministic and able to be
   reversed to satisfy the previous requirement.

   +-------+              +-------------+              +--------+
   | LDAP  |              | HTTP server |              | Client |
   |       |              |             | <- Login --  |        |
   |       | <-- Bind --  |             |              |        |
   |       | - Success -> |             |              |        |
   |       | <- Req Token |             |              |        |
   |       | -- Token --> |             |              |        |
   |       | <- Unbind -  |             |              |        |
   |       | - Success -> |             |              |        |
   |       |              | Html Escape |              |        |
   |       |              |             | -- Safe -->  |        |
   |       |              |             |     Token    |        |
   |       |              |             |              | Store  |
   |       |              |             | < Request +- |        |
   |       |              | Reverse esc |    Token     |        |
   |       | < Token Bind |             |              |        |
   |       | - Success -> |             |              |        |
   |       | <- Operation |             |              |        |
   |       | <- Unbind -  |             |              |        |
   |       | - Success -> |             |              |        |
   |       |              |             | - Response > |        |
   +-------+              +-------------+              +--------+

                                 Figure 4

   This example shows how a client is issued with a token when
   communicating with a web server via the HTTP intermediate.  The
   Client does not need to be aware of the SASL/LDAP system in the
   background, or the token's formatting rules.  Provided the HTTP



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   server in proxy, if required to transform the token, is able to undo
   the transformations, this is a valid scenario.  For example, HTML
   escaping a base64 token.

4.3.  SASL Authentication

   The client issues a SASL bind request with the mechanism name
   LDAPSSOTOKEN.

   The client sends an appropriate authid in RFC 2078 [RFC2078] form.

   The client provides the encrypted token that was provided in the
   LDAPSSOTokenResponse Token Field.

   The token is decrypted and authenticated based on the token format
   selected by the server.  The server MAY attempt multiple token keys
   and or formats to find the correct issuing format and key.

   If the token decryption fails, the attempt with this key and format
   MUST be considered to fail.

   If the values have been tampered with, IE hash authentication fails,
   the attempt with the key and format MUST be considered to fail.

   The token decryption MUST return a valid DateTimeUntil,
   DateTimeIssued and User Unique Id.  If this is not returned, the
   decryption MUST be considered to fail.

   If all token formats and keys fail to decrypt, this MUST cause an
   invalidCredentials error.

   The DateTimeUntil field is checked against the servers current time.
   If the current time exceeds or is equal to DateTimeUntil,
   invalidCredentials MUST be returned.

   The User Unique Id is validated to exist on the server.  If the User
   Unique Id does not exist, invalidCredentials MUST be returned.

   The authid provided by the SASL client is verified with the User
   Unique Id.  For example if the authid is william@EXAMPLE.COM, the
   server maps this to an identity.  Once this identity is validated,
   the identity is check to match the User Unique Id.  If they do not
   match, the authentication MUST fail.

   The DateTimeIssued field is validated against the User Unique Id
   object's attribute or related attribute that contains "Valid Not
   Before".  If the value of "Valid Not Before" exceeds or is equal to
   DateTimeIssued, invalidCredentials MUST be returned.



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   Only if all of these steps have succeeded, then the authentication is
   considered successful.

4.4.  Valid Not Before Attribute

   The management and details of the "Valid Not Before" attribute are
   left to the implementation to decide how to implement and manage.
   The implementation should consider how an administrator or
   responsible party could revoke tokens for users other than their own.
   The Valid Not Before SHOULD be replicated between LDAP servers to
   allow correct revocation across many LDAP servers.  For example,
   Valid Not Before MAY be an attribute on the User Unique Id object, or
   MAY be on another object with a unique relation to the User Unique
   Id.

5.  LDAP Component

5.1.  Token Generation

   An ldap extended operation is issued as per Section 4.12 of RFC 4511
   [RFC4511].

   The LDAP OID to be used for the LDAPSSOTokenRequest is
   2.16.840.1.113730.3.5.14.

   The LDAP OID to be used for the LDAPSSOTokenResponse is
   2.16.840.1.113730.3.5.15.

   A User Unique Id is selected.  This may be the Bind DN, UUID or other
   utf8 identifier that uniquely determines an object.

   The extended operation must fail if the LDAP connection security
   stregth factors is 0.

   Tokens must not be generated for Anonymous binds.  This means, tokens
   may only be generated for connections with a valid bind dn set.

   Token requests MUST contain a requested lifetime in seconds.  The
   server MAY choose to ignore this lifetime and set it's own value.

   A token request of a negative or zero value SHOULD default to a
   server definied minimum lifetime.

   The token is created as per an example token format in 4.1.  This
   value is then encrypted with an encryption algorithm of the servers
   choosing.  The client does not need to be aware of the encryption
   algorithm.




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   The DateTimeIssued, DateTimeUntil and User Unique Id are collected in
   the format required by the token format we are choosing to use in the
   server.  The token is then generated by the chosen algorithm.

   The encrypted token is sent to the client in the LDAPSSOTokenResponse
   structure, along with the servers chosen valid life time as a guide
   for the client to approximate the expiry of the token.  This valid
   life time value is in seconds.

   If the token cannot be generated due to a server error,
   LDAP_OPERATION_ERROR MUST be returned.

5.1.1.  Token Generation Extended Operation

   LDAPSSOTokenRequest ::= SEQUENCE {
       ValidLifeTime INTEGER }

   LDAPSSOTokenResponse ::= SEQUENCE {
       ValidLifeTime INTEGER,
       EncryptedToken         OCTET STRING
   }

                                 Figure 5

5.2.  Token Revocation

   An ldap extended operation is issued as per Section 4.12 RFC 4511
   [RFC4511].

   The LDAP OID to be used for LDAPSSOTOKENRevokeRequest is
   2.16.840.1.113730.3.5.16.

   The extended operation MUST fail if the connection is anonymous.

   The extended operation MUST fail if the LDAP connection security
   strength factors is 0.

   The extended operation MUST only act upon the "Valid Not Before"
   attribute related to the bind DN of the connection.

   Upon recieving the extended operation to revoke tokens, the directory
   server MUST set the current BindDN's related "Valid Not Before"
   attribute timestamp to the current datetime.  This will have the
   effect, that all previously issued tokens are invalidated.

   This revocation option must work regardless of directory server
   access controls on the attribute containing "Valid Not Before".




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5.2.1.  Token Revocation Extended Operation

   The extended operation requestValue MUST not be set for LDAP SSO
   Token revocation.

   The extended operation does not provide a response OID.  The result
   is set in the LDAPResult.

5.3.  Binding

   The SASL bind attempt MUST fail if the LDAP connection security
   strength factors is 0.

   The SASL Authentication is attempted as per Section 4.3.  If this
   does not succeed, the bind attempt MUST fail.

   The LDAP Object is retrived from the User Unique Id, and a Bind DN
   Determined.  If no Bind DN can be determined, the bind attempt MUST
   fail.

   The current Bind DN MUST be set to the Bind DN of the LDAP object
   that is determined, and the result ldap success is returned to the
   LDAP client.

6.  Security Considerations

   Due to the design of this token, it is possible to use it in a replay
   attack.  Notable threats are storage on the client and man in the
   middle attacks.  To minimise the man in the middle attack thread,
   LDAP security strength factor of greater than 0 is a requirement.
   Client security is not covered by this document.

7.  Requirements

   The SASL mechanism, LDAPSSOTOKEN, MUST be registered to IANA as per
   RFC 2222 [RFC2222] Section 6.4

8.  References

8.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.






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8.2.  Informative References

   [FERNETSPEC]
              Maher, T. and K. Rarick, "Fernet Specification", 2013,
              <https://github.com/fernet/spec/blob/master/Spec.md>.

   [RFC2078]  Linn, J., "Generic Security Service Application Program
              Interface, Version 2", RFC 2078, DOI 10.17487/RFC2078,
              January 1997, <http://www.rfc-editor.org/info/rfc2078>.

   [RFC2222]  Myers, J., "Simple Authentication and Security Layer
              (SASL)", RFC 2222, DOI 10.17487/RFC2222, October 1997,
              <http://www.rfc-editor.org/info/rfc2222>.

   [RFC4511]  Sermersheim, J., Ed., "Lightweight Directory Access
              Protocol (LDAP): The Protocol", RFC 4511,
              DOI 10.17487/RFC4511, June 2006,
              <http://www.rfc-editor.org/info/rfc4511>.

Authors' Addresses

   William Brown
   Red Hat Asia-Pacific Pty Ltd
   Level 1, 193 North Quay
   Brisbane, Queensland  4000
   AU

   Email: wibrown@redhat.com


   Simo Sorce (editor)
   Red Hat, Inc.

   Email: simo@redhat.com


   Kieran Andrews (editor)
   The University of Adelaide
   Adelaide, South Australia  5005
   AU

   Email: kieran.andrews@adelaide.edu.au









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