Network Working Group J. Myers Internet Draft Carnegie Mellon Document: draft-myers-imap-acl-00.txt December 1995 IMAP4 ACL extension Status of this Memo This document is an Internet Draft. 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. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a ``working draft'' or ``work in progress''. To learn the current status of any Internet-Draft, please check the 1id-abstracts.txt listing contained in the Internet-Drafts Shadow Directories on ds.internic.net, nic.nordu.net, ftp.isi.edu, or munnari.oz.au. A revised version of this draft document will be submitted to the RFC editor as a Proposed Standard for the Internet Community. Discussion and suggestions for improvement are requested. This document will expire before April 1996. Distribution of this draft is unlimited. J. Myers [Page i]
Internet DRAFT ACL December 14, 1995 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 an ASCII string with implementation-defined semantics. Possible variations of identifier interpretation include, but are not limited to: * User names, as specified in the LOGIN command. * Named groups of users, presumably managed by some authorization service. * Only allowing identifiers supported by the operating system (e.g. ``user'', ``group'', and ``other'' for the Unix filesystem) * A prefix to the identifier specifying an "authentication type". As an example, an implementation may control posting to a group based on the contents of the From: header: from$user p * Whether the union of rights for matching identifiers are granted to a user or whether the rights for the most specific matching identifier is granted. As an example, for a mailbox with the following ACL: user lrsa group-user-is-in lrsw J. Myers [Page 2]
Internet DRAFT ACL December 14, 1995 One implementation may grant the user 'lrswa' rights, another may only grant the user 'lrsa' rights. * A prefix to an identifier name specifying the listed rights are to be removed from users who match the prefixed identifier. As an example, for a mailbox with the following ACL: group-user-is-in lrsw -user w An implementation may grant the user 'lrs' rights. 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. Digits are reserved for implementation or site defined rights. The 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. For example, in an implementation that uses unix mode bits, the rights "wisd" are tied, the "a" right is always granted to the owner and is never granted to another user. If rights are tied in an implementation, it should be conservative in granting rights in response to SETACL commands--unless all rights in a tied set are specified, none should be used. Numeric rights may not be tied. J. Myers [Page 3]
Internet DRAFT ACL December 14, 1995 4. Commands 4.1. SETACL MAILBOX Arguments: mailbox name authentication identifier access rights Data: no specific data for this command Result: OK - setacl mailbox completed NO - setacl mailbox failure: can't set acl BAD - command unknown or arguments invalid The SETACL MAILBOX command changes the access control list on the specified mailbox so that the specified identifier is granted the permissions enumerated in rights. 4.2. DELETEACL MAILBOX Arguments: mailbox name authentication identifier Data: no specific data for this command Result: OK - deleteacl mailbox completed NO - deleteacl mailbox failure: can't delete acl BAD - command unknown or arguments invalid Removes any portion of the access control list for mailbox for the specified identifier. 4.3. GETACL MAILBOX Arguments: mailbox name Data: untagged responses: ACL MAILBOX Result: OK - getacl mailbox completed NO - getacl mailbox failure: can't get acl BAD - command unknown or arguments invalid The GETACL MAILBOX command returns the access control list for mailbox in some set of untagged ACL replies. There may not be J. Myers [Page 4]
Internet DRAFT ACL December 14, 1995 more than one ACL reply specifying any given identifier. Example: C: A002 GETACL MAILBOX INBOX S: * ACL MAILBOX INBOX Fred rwipslda S: A002 Ok Getacl complete 4.4. MYRIGHTS MAILBOX Arguments: mailbox name Data: untagged responses: MYRIGHTS MAILBOX Result: OK - myrights mailbox completed NO - myrights mailbox failure: can't get rights BAD - command unknown or arguments invalid The MYRIGHTS MAILBOX command returns the set of rights that the user has to mailbox in an untagged MYRIGHTS reply. 5. Responses 5.1. ACL MAILBOX Data: mailbox name identifier rights The ACL MAILBOX response occurs as a result of a GETACL MAILBOX command. The first string is the mailbox name for which this ACL entry applies. The second string is the identifier for which this entry applies. The third string is the set of rights that the identifier has. 5.2. MYRIGHTS MAILBOX Data: mailbox name rights The MYRIGHTS MAILBOX response occurs as a result of a MYRIGHTS MAILBOX command. The first string is the mailbox name for which this ACL entry applies. The second string is the set of rights that the client has. J. Myers [Page 5]
Internet DRAFT ACL December 14, 1995 6. Formal Syntax The following syntax specification uses the augmented Backus-Naur Form (BNF) notation as specified in [RFC-822] with one exception; the delimiter used with the "#" construct is a single space (SPACE) and not one or more commas. 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 acl_option SPACE astring SPACE astring SPACE astring acl_option ::= "MAILBOX" deleteacl ::= "DELETEACL" SPACE acl_option SPACE astring SPACE astring getacl ::= "GETACL" SPACE acl_option SPACE astring myrights ::= "MYRIGHTS" SPACE acl_option SPACE astring myrights_data ::= "MYRIGHTS" acl_option SPACE astring SPACE astring setacl ::= "SETACL" SPACE acl_option SPACE astring SPACE astring SPACE astring 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. 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. J. Myers [Page 6]
Internet DRAFT ACL December 14, 1995 9. Author's Address John G. Myers Carnegie-Mellon University 5000 Forbes Ave. Pittsburgh PA, 15213-3890 Email: jgm+@cmu.edu J. Myers [Page 7]
Internet DRAFT ACL December 14, 1995 Table of Contents Status of this Memo ............................................... i 1. Abstract ..................................................... 2 2. Conventions Used in this Document ............................ 2 3. Introduction and Overview .................................... 2 4. Commands ..................................................... 4 4.1. SETACL MAILBOX ............................................... 4 4.2. DELETEACL MAILBOX ............................................ 4 4.3. GETACL MAILBOX ............................................... 4 4.4. MYRIGHTS MAILBOX ............................................. 5 5. Responses .................................................... 5 5.1. ACL MAILBOX .................................................. 5 5.2. MYRIGHTS MAILBOX ............................................. 5 6. Formal Syntax ................................................ 6 7. References ................................................... 6 8. Security Considerations ...................................... 6 9. Author's Address ............................................. 7 J. Myers [Page ii]