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Network Working Group                                           J. MyersRequest for Comments: 2086                               Carnegie MellonCategory: Standards Track                                   January 1997IMAP4 ACL extensionStatus 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.1.   Abstract   The ACL extension of the Internet Message Access Protocol [IMAP4]   permits access control lists to be manipulated through the IMAP   protocol.Table of Contents1.   Abstract...............................................12.   Conventions Used in this Document......................13.   Introduction and Overview..............................24.   Commands...............................................34.1. SETACL.................................................34.2. DELETEACL..............................................44.3. GETACL.................................................44.4. LISTRIGHTS.............................................44.5. MYRIGHTS...............................................55.   Responses..............................................55.1. ACL....................................................55.2. LISTRIGHTS.............................................65.3. MYRIGHTS...............................................66.   Formal Syntax..........................................67.   References.............................................78.   Security Considerations................................79.   Author's Address.......................................82.   Conventions Used in this Document   In examples, "C:" and "S:" indicate lines sent by the client and   server respectively.Myers                       Standards Track                     [Page 1]

RFC 2086                     ACL extension                  January 19973.   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 US-ASCII 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.   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'' 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 (CREATE new sub-mailboxes in any implementation-defined       hierarchy)   d - delete (STORE DELETED flag, perform EXPUNGE)   a - administer (perform SETACL)   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.Myers                       Standards Track                     [Page 2]

RFC 2086                     ACL extension                  January 1997   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".  How these rights are combined 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.  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.   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.  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".  Implementations   need not support having identifiers which start with a dash in ACLs.4.   Commands4.1. 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.Myers                       Standards Track                     [Page 3]

RFC 2086                     ACL extension                  January 19974.2. 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.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               S: A002 OK Getacl complete4.4. 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.Myers                       Standards Track                     [Page 4]

RFC 2086                     ACL extension                  January 1997   Example:    C: a001 LISTRIGHTS ~/Mail/saved smith               S: * LISTRIGHTS ~/Mail/saved smith la r swicd               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               0 1 2 3 4 5 6 7 8 94.5. 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               S: A003 OK Myrights complete5.   Responses5.1. 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.Myers                       Standards Track                     [Page 5]

RFC 2086                     ACL extension                  January 19975.2. 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.      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.Myers                       Standards Track                     [Page 6]

RFC 2086                     ACL extension                  January 1997   acl_data        ::= "ACL" SPACE mailbox *(SPACE identifier SPACE                        rights)   deleteacl       ::= "DELETEACL" SPACE mailbox SPACE identifier   getacl          ::= "GETACL" SPACE mailbox   identifier      ::= astring   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                           ;; rights to replace   myrights        ::= "MYRIGHTS" SPACE mailbox   myrights_data   ::= "MYRIGHTS" SPACE mailbox SPACE rights   rights          ::= astring   setacl          ::= "SETACL" SPACE mailbox SPACE identifier                       SPACE mod_rights7.   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 822.8.   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.Myers                       Standards Track                     [Page 7]

RFC 2086                     ACL extension                  January 19979.   Author's Address   John G. Myers   Carnegie-Mellon University   5000 Forbes Ave.   Pittsburgh PA, 15213-3890   Email: jgm+@cmu.eduMyers                       Standards Track                     [Page 8]