NetworkIMAPEXT Working Group                                           J. Myers                                        A. Melnikov
Internet Draft                                   Netscape Communications                                                    Editor
Document: draft-ietf-imapext-acl-00.txt                         May 2000 draft-ietf-imapext-acl-01.txt                    November 2001

                          IMAP4 ACL extension

Status of this Memo

   This document is an Internet Draft and is in full conformance with
   all provisions of Section 10 of RFC 2026.

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   A revised version of this draft document will be submitted to the RFC
   editor as a Proposed Standard for the Internet Community.  Discussion
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   draft is unlimited.

Internet DRAFT                    ACL                       May 23, 2000

0.   Open issues

   This section will be removed when the draft will be published as RFC.
   It is intended to simplify discussion.

    1). Should the document define exact syntax for identifiers starting
        with '$'? For example, the following was proposed by Mark Crispin:

      Definable identifiers.  Server implementations are *NOT* required to
      use any of these, but if they do, these are their semantics.  Note
      that definable identifiers may expand to other definable identifiers.

      $G$xxx	global identifier xxx.  Valid everywhere
      $U$xxx	per-user identifier xxx.  Valid only for the logged-in user
      $M$xxx	per-mailbox identifer xxx.  Valid only for this mailbox
      $xxxxx	reserved for future definition

      Non-definable identifiers.  Server implementations SHOULD support $WORLD,
      and MUST support anyone and user names.  However, a server can respond
      with a NO.

      $WORLD		all authorized users but not anonymous
      $ANONYMOUS		anonymous users
      $DISABLE		disabled rights

    2). Should the document define additional capabilities for servers that
        implement "union of positive rights minus union of negative rigths"?
        Or maybe add capability for implementations that use the most specific
        rights?

    3). Do we need a mechanism to encode login names if they start with
        $, dash?

    4). Drop identifiers starting with dash?

1.   Abstract

   The ACL extension of the Internet Message Access Protocol [IMAP4]
   permits access control lists to be manipulated through the IMAP
   protocol.

2.   Conventions Used in this Document

   In examples, "C:" and "S:" indicate lines sent by the client and
   server respectively.

3.   Introduction and Overview

   The ACL extension is present in any IMAP4 implementation which
   returns "ACL" as one of the supported capabilities to the CAPABILITY
   command.

   An access control list is a set of <identifier,rights> pairs.

   Identifier is a UTF-8 string.  The identifier "anyone" is reserved to
   refer to the universal identity (all authentications, including
   anonymous).  All user name strings accepted by the LOGIN or
   AUTHENTICATE commands to authenticate to the IMAP server are reserved
   as identifiers for the corresponding user.  Identifiers starting with
   a dash ("-") are reserved for "negative rights", described below.
   Identifiers starting with a dollar sign ("$") are reserved for
   groups.
   groups and implementation defined aliases.  All other identifier strings
   are interpreted in an implementation-defined manner.

   Rights is a string listing a (possibly empty) set of alphanumeric
   characters, each character listing a set of operations which is being
   controlled.  Letters are reserved for ``standard'' ''standard'' rights, listed
   below.  The set of standard rights may only be extended by a
   standards-track document.  Digits are reserved for implementation or
   site defined rights.  The currently defined standard rights are:

   l - lookup (mailbox is visible to LIST/LSUB commands)
   r - read (SELECT the mailbox, perform CHECK, FETCH, PARTIAL,
       SEARCH, COPY from mailbox)
   s - keep seen/unseen information across sessions (STORE \SEEN flag)
   w - write (STORE flags other than \SEEN and \DELETED)
   i - insert (perform APPEND, COPY into mailbox)
   p - post (send mail to submission address for mailbox,
       not enforced by IMAP4 itself)
   c - create and delete mailbox mailboxes (CREATE new sub-mailboxes in any
       implementation-defined hierarchy, RENAME or DELETE mailbox) parent mailbox for the new
       mailbox name in RENAME).
       When a new mailbox is created it SHOULD inherit rights from
       the parent mailbox (if one exists) in the defined hierarchy.
   x - delete mailbox (DELETE mailbox, old mailbox name in RENAME)
   d - delete messages (STORE \DELETED flag, flag)
   e - perform EXPUNGE) EXPUNGE
   a - administer (perform SETACL)

Internet DRAFT                    ACL                       May 23, 2000

   Note, that moving (RENAME command) mailbox from one parent to another
   requires "x" right on the mailbox itself and "c" right for the new parent.
   For example, if the user wants to rename mailbox named "A/B/C"
   ("/" is hierarchy separator) to "D/E", the user must have "x" right
   for mailbox "A/B/C" and "c" right for mailbox "D".

   An implementation may tie rights together or may force rights to
   always or never be granted to particular identifiers.  For example,
   in an implementation that uses unix mode bits, the rights "wisd" are
   tied, the "a" right is always granted to the owner of a mailbox and
   is never granted to another user.  If rights are tied in an
   implementation, the implementation must be conservative in granting
   rights in response to SETACL commands--unless all rights in a tied
   set are specified, none of that set should be included in the ACL
   entry for that identifier.  A client may discover the set of rights
   which may be granted to a given identifier in the ACL for a given
   mailbox by using the LISTRIGHTS command.

   When an identifier in an ACL starts with a dash ("-"), that indicates
   that associated rights are to be removed from the identifier that is
   prefixed by the dash. This is referred to as a "negative right". For
   example, if the identifier "-fred" is granted the "w" right, that
   indicates that the "w" right is to be removed from users matching the
   identifier "fred".  Server implementations are not required to
   support having identifiers which start with a dash in ACLs.

   It is possible for multiple identifiers in an access control list to
   apply to a given user (or other authentication identity).  For
   example, an ACL may include rights to be granted to the identifier
   matching the user, one or more implementation-defined identifiers
   matching groups which include the user, and/or the identifier
   "anyone".  These How these rights are combined by taking to determine the user's
   access is implementation-defined.  An implementation may choose, for
   example, to use the union of the rights granted to the applicable
   identifiers and then removing minus the union of the negative rights applying
   to the applicable identifiers. An implementation may instead choose,
   for example, to only use those rights granted to the most specific
   identifier present in the ACL. A client may determine the set of rights
   granted to the logged-in user for a given mailbox by using the MYRIGHTS
   command.

Internet DRAFT                    ACL                       May 23, 2000

4.   Commands

4.1. SETACL

   Arguments:  mailbox name
               authentication identifier
               access right modification

   Data:       no specific data for this command

   Result:     OK - setacl completed
               NO - setacl failure: can't set acl
               BAD - command unknown or arguments invalid

      The SETACL command changes the access control list on the
      specified mailbox so that the specified identifier is granted
      permissions as specified in the third argument.

      The third argument is a string containing an optional plus ("+")
      or minus ("-") prefix, followed by zero or more rights characters.
      If the string starts with a plus, the following rights are added
      to any existing rights for the identifier.  If the string starts
      with a minus, the following rights are removed from any existing
      rights for the identifier.  If the string does not start with a
      plus or minus, the rights replace any existing rights for the
      identifier.

4.2. DELETEACL

   Arguments:  mailbox name
               authentication identifier

   Data:       no specific data for this command

   Result:     OK - deleteacl completed
               NO - deleteacl failure: can't delete acl
               BAD - command unknown or arguments invalid

      The DELETEACL command removes any <identifier,rights> pair for the
      specified identifier from the access control list for the
      specified mailbox.

Internet DRAFT                    ACL                       May 23, 2000

4.3. GETACL

   Arguments:  mailbox name

   Data:       untagged responses: ACL

   Result:     OK - getacl completed
               NO - getacl failure: can't get acl
               BAD - command unknown or arguments invalid

      The GETACL command returns the access control list for mailbox in
      an untagged ACL reply.

   Example:    C: A002 GETACL INBOX
               S: * ACL INBOX Fred rwipslda rwipslexda
               S: A002 OK Getacl complete

4.4. LISTRIGHTS

   Arguments:  mailbox name
               authentication identifier

   Data:       untagged responses: LISTRIGHTS

   Result:     OK - listrights completed
               NO - listrights failure: can't get rights list
               BAD - command unknown or arguments invalid

      The LISTRIGHTS command takes a mailbox name and an identifier and
      returns information about what rights may be granted to the
      identifier in the ACL for the mailbox.

   Example:    C: a001 LISTRIGHTS ~/Mail/saved smith
               S: * LISTRIGHTS ~/Mail/saved smith la r swicd swi cdex
               S: a001 OK Listrights completed

               C: a005 LISTRIGHTS archive.imap anyone
               S: * LISTRIGHTS archive.imap anyone "" l r s w i p c d a e x
               0 1 2 3 4 5 6 7 8 9
               S: a005 OK Listrights completed

Internet DRAFT                    ACL                       May 23, 2000

4.5. MYRIGHTS

   Arguments:  mailbox name

   Data:       untagged responses: MYRIGHTS

   Result:     OK - myrights completed
               NO - myrights failure: can't get rights
               BAD - command unknown or arguments invalid

      The MYRIGHTS command returns the set of rights that the user has
      to mailbox in an untagged MYRIGHTS reply.

   Example:    C: A003 MYRIGHTS INBOX
               S: * MYRIGHTS INBOX rwipslda rwipsldexa
               S: A003 OK Myrights complete

5.   Responses

5.1. ACL

   Data:       mailbox name
               zero or more identifier rights pairs

      The ACL response occurs as a result of a GETACL command.  The
      first string is the mailbox name for which this ACL applies.  This
      is followed by zero or more pairs of strings, each pair contains
      the identifier for which the entry applies followed by the set of
      rights that the identifier has.

5.2. LISTRIGHTS

   Data:       mailbox name
               identifier
               required rights
               list of optional rights

      The LISTRIGHTS response occurs as a result of a LISTRIGHTS
      command.  The first two strings are the mailbox name and
      identifier for which this rights list applies.  Following the
      identifier is a string containing the (possibly empty) set of
      rights the identifier will always be granted in the mailbox.

Internet DRAFT                    ACL                       May 23, 2000
      Following this are zero or more strings each containing a set of
      rights the identifier may be granted in the mailbox.  Rights
      mentioned in the same string are tied together--either all must be
      granted to the identifier in the mailbox or none may be granted.

      The same right may not be listed more than once in the LISTRIGHTS
      command.

5.3. MYRIGHTS

   Data:       mailbox name
               rights

      The MYRIGHTS response occurs as a result of a MYRIGHTS command.
      The first string is the mailbox name for which these rights apply.
      The second string is the set of rights that the client has.

6.   Formal Syntax

   The following syntax specification uses the augmented Backus-Naur
   Form (BNF) notation as specified in [RFC-822] as modified by [IMAP4].
   Non-terminals referenced but not defined below are as defined by
   [IMAP4].

   Except as noted otherwise, all alphabetic characters are
   case-insensitive.  The use of upper or lower case characters to
   define token strings is for editorial clarity only.  Implementations
   MUST accept these strings in a case-insensitive fashion.

   acl_data        ::= "ACL" SPACE mailbox *(SPACE identifier SPACE rights)

   deleteacl       ::= "DELETEACL" SPACE mailbox SPACE identifier

   getacl          ::= "GETACL" SPACE mailbox

   identifier      ::= astring
                           ;; UTF-8

   listrights      ::= "LISTRIGHTS" SPACE mailbox SPACE identifier

   listrights_data ::= "LISTRIGHTS" SPACE mailbox SPACE identifier
                           SPACE rights *(SPACE rights)

   mod_rights      ::= astring
                           ;; +rights to add, -rights to remove

Internet DRAFT                    ACL                       May 23, 2000

                           ;; rights to replace

   myrights        ::= "MYRIGHTS" SPACE mailbox

   myrights_data   ::= "MYRIGHTS" SPACE mailbox SPACE rights

   rights          ::= astring

   setacl          ::= "SETACL" SPACE mailbox SPACE identifier SPACE mod_rights

7.   References

   [IMAP4] Crispin, M., "Internet Message Access Protocol - Version 4",
   RFC 1730, University of Washington, December 1994.

   [RFC-822] Crocker, D., "Standard for the Format of ARPA Internet Text
   Messages", STD 11, RFC 822.

   [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISP IS0 10646",
   RFC 2279.

8.   Security Considerations

   An implementation must make sure the ACL commands themselves do not
   give information about mailboxes with appropriately restricted ACL's.
   For example, a GETACL command on a mailbox for which the user has
   insufficient rights should not admit the mailbox exists, much less
   return the mailbox's ACL.

9.   Author's Address Aknowledgement

   This document is a revision of the RFC 2086 written by John G. Myers
   Carnegie-Mellon University
   5000 Forbes Myers.

   Editor also appreciate comments received from Mark Crispin, Chris Newman,
   Curtis King, Lyndon Nerenberg and other members of IMAPEXT working group.

10.   Editor's Address

   Alexey Melnikov
   mailto: Alexey.Melnikov@messagingdirect.com

   ACI WorldWide/MessagingDirect
   900 10117 - Jasper Ave.
   Pittsburgh PA, 15213-3890

   Email: jgm+@cmu.edu
   Edmonton, Alberta, T5J 1W8, CANADA

Appendix A. Changes since RFC 2086

   1. Changed the charset of "identifier" from US-ASCII to UTF-8 UTF-8.

   2. Specified that identifiers starting with a dollar sign ("$") are
      reserved for groups and implementation defined aliases.

   3. Specified that mailbox deletion is controled by the "c" "x" right and
      EXPUNGE is controlled by "e" right.

Internet DRAFT                    ACL                       May 23, 2000

   4. Required servers to implement "union of rights minus union of
      negative rights" Clarified that RENAME requires "c" right for evaluating ACLs.

Internet DRAFT                    ACL                       May 23, 2000

                           TTTTaaaabbbblllleeee ooooffff CCCCoooonnnntttteeeennnnttttssss

Status of this Memo ...............................................    i
1.   Abstract .....................................................    2
2.   Conventions Used in this Document ............................    2
3.   Introduction the new parent and Overview ....................................    2
4.   Commands .....................................................    4
4.1. SETACL .......................................................    4
4.2. DELETEACL ....................................................    4
4.3. GETACL .......................................................    4
4.4. LISTRIGHTS ...................................................    5
4.5. MYRIGHTS .....................................................    5
5.   Responses ....................................................    6
5.1. ACL ..........................................................    6
5.2. LISTRIGHTS ...................................................    6
5.3. MYRIGHTS .....................................................    7
6.   Formal Syntax ................................................    7
7.   References ...................................................    8
8.   Security Considerations ......................................    8
9.   Author's Address .............................................    8
Appendix A. Changes since RFC 2086 ................................    8 "x"
      right for the old name.