IMAPEXT Working Group A. Melnikov Internet Draft Editor Document: draft-ietf-imapext-acl-07.txt February 2003 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. 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 ``work in progress''. The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 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. Distribution of this draft is unlimited. 0. Open issues and ToDo list This section will be removed when the draft will be published as RFC. It is intended to simplify discussion. 1). Require support for special identifier "disabled" for "ACL2=MOST-SPECIFIC" model? 2). "ACL2=MOST-SPECIFIC" model: If a user belongs to multiple groups, document how rights are calculated. 3). IANA registry for <vendorname> prefix in identifiers? 4). ACL2 interaction with QUOTA extension should be moved to "QUOTA=" document? 5). Do we need the following functionality: discover the set of rights which may be granted to a given identifier in the ACL for a given mailbox? 6). There is a proposal to replace MYRIGHT with either ACL FETCH or ACL CHECK: ACL FETCH is slightly different than MYRIGHTS in that it takes an identifier as an argument and returns the rights for that identifier (?? is this desirable ??). Or perhaps there could be an ACL CHECK that, given an identifier and a set of right, returns whether or not that identifier has those rights. ACL CHECK is probably more useful. For now MYRIGHTS is left as is, because neither parameters, nor responses were affected by the change to identifiers. However, if there is a desire to accept multiple mailboxes or mailbox masks in MYRIGHT, it would be better to change it to ACL <something> as well. 7). Cleanup appendix A before publication as RFC, as some changes don't apply to RFC 2086. 8). Other editorial comments/questions are enclosed in << and >>. Table of Contents 1 Abstract .................................................. X 2 Conventions Used in this Document ......................... X 3 Introduction and Overview ................................. X 3.1 Access Control ........................................... X 3.2 Access calculation model ................................. X 3.3 Rights required to perform different IMAP4rev1 commands .. X 4 ACL manipulation commands ................................. X 4.1 ACL STORE ................................................ X 4.2 ACL DELETE ............................................... X 4.3 ACL SET .................................................. X 4.4 ACL GET .................................................. X 4.5 MYRIGHTS ................................................. X 5 ACL related responses ..................................... X 5.1 Extended LIST response with ACL information .............. X 5.2 RIGHTS-INFO .............................................. X 5.3 ACLFAILED untagged response .............................. X 5.4 MYRIGHTS untagged response ............................... X 5.5 MYRIGHTS response code ................................... X 6 Formal Syntax ............................................. X 7 IANA considerations ....................................... X 7.1 ACL access calculation rule Registration Template ........ X 7.2 Initial Registrations .................................... X 7.2.1 Registration: UNION access calculation rule ............ X 7.2.2 Registration: MOST-SPECIFIC access calculation rule .... X 8 Security Considerations ................................... X 9 Other considerations ...................................... X 9.1 Compatibility with RFC 2086 .............................. X 9.2 ACL2 interaction with QUOTA extension .................... X 9.3 Mapping of ACL rights to READ-WRITE and READ-ONLY response codes ........................................... X 9.4 Additional requirements and Implementation notes ......... X 10 Normative References ..................................... X 11 Informative References ................................... X 12 Aknowledgement ........................................... X 13 Editor's Address ......................................... X 14 Full Copyright Statement ................................. X 1. Abstract The ACL (Access Control List) extension of the Internet Message Access Protocol [IMAP4] permits mailbox 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. In all examples "/" character is used as hierarchy separator. 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 [KEYWORDS]. 3. Introduction and Overview The ACL (Access Control List) extension of the Internet Message Access Protocol [IMAP4] permits mailbox access control lists to be retrieved and manipulated through the IMAP protocol. The ACL extension is present in any IMAP4 implementation which returns a capability starting with "ACL2=" prefix as one of the supported capabilities to the CAPABILITY command. The prefix is followed by "rule identifier" as described in 7.1. The document contains the following parts: section 3.1 provides the definition of different classes of identifiers and defines standard rights; section 3.2 introduces access calculation model, i.e. it describes how to calculate from an ACL which rigths apply to a particular user; section 3.3 summarizes relationship of different access rights with IMAP commands; section 4 introduces new IMAP commands the client can use to manipulate ACLs; section 5 defines new ACL related responses; and section 9 lists important considerations for compatibility with [IMAP4], RFC 2086 and some IMAP extensions. 3.1. Access Control An access control list is a set of <identifier,rights> pairs. An ACL applies to a mailbox. Identifier is a UTF-8 string. An identifier may have one of the following forms: a). "anyone" - special identifier that refers to the universal identity (all authentications, including anonymous). b). "authuser" - special identifier that refer to all authenticated users, but not anonymous. c). "owner" - special identifier that refers to the owner of a mailbox (if any). d). "administrators" - special identifier that refers to all users with administrative rights for the server. e). "user=<username>" - refers to a user. Here "<username>" is a user name string accepted by the LOGIN or AUTHENTICATE commands. f). "group=<groupname>" - refers to a group. Here "<groupname>" is a group name. g). "vendor=<vendorname>.<xxx>" - refers to a vendor specific special identifier, not covered by a).-f). h). "-<identifier>", where <identifier> is one of a).-g). This is reserved for "negative rights", described below. Note that a server is not required to implement any special identifier mentioned above. However if it allows a user to perform ACL operations on any one of them, server MUST use the semantic as described above. All other identifier names are reserved for future definition in an extension or revision to this specification (also known as ACL2). 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, SUBSCRIBE mailbox) r - read (SELECT the mailbox, perform STATUS, CHECK, FETCH, SEARCH, COPY from mailbox) s - keep seen/unseen information across sessions (set or clear \SEEN flag via STORE, APPEND or COPY) w - write (set or clear flags other than \SEEN and \DELETED via STORE, APPEND or COPY) i - insert (perform APPEND, COPY into mailbox) p - post (send mail to submission address for mailbox, not enforced by IMAP4 itself) c - create mailboxes (CREATE new sub-mailboxes in any implementation-defined hierarchy, 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) t - delete messages (set or clear \DELETED flag via STORE, set \DELETED flag during APPEND/COPY) e - perform EXPUNGE and expunge as a part of CLOSE d - This right is defined for backward compatibility with ACL extension (RFC 2086). If a client sets "d" right, the server MUST set "x", "e" and "t" rights. When the client clears the "d" right, the server MUST clear "x", "e" and "t" rights. When all three of "x", "e" and "t" are set, the server MUST return "d" right in response to an ACL GET command. If "x", "e" and "t" rights are not tied together, "d" right MUST NOT be returned in a RIGHTS-INFO response. a - administer (perform ACL STORE, ACL SET and ACL DELETE) 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 ACL STORE commands--unless all rights in a tied set are specified, none of that set should be included in the ACL entry for that identifier. If the server fails an ACL modification command (ACL STORE or ACL SET) because some rights are tied, it MUST return RIGHTS-INFO untagged response (see section 5.2). 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". This differs from ACL DELETE in that a negative right is added to the ACL, and is part of the calculation of the rights. For example, if the identifier "-user=fred" is granted the "w" right, that indicates that the "w" right is to be removed from users matching the identifier "user=fred", even though the user "fred" might have the "w" right as a consequence of some other identifier in the ACL. A ACL DELETE of "user=fred" simply deletes the identifier "user=fred" from the ACL; it does not affect any rights that the user "fred" may get from another ACL. Server implementations are not required to support "negative right" identifiers. 3.2. Access calculation model 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. The set of rules that describes how access is calculated is defined by a rule identifier (rule-ID). This document doesn't define any commands for manipulating a group membership. A client may determine the set of rights granted to the logged-in user for a given mailbox by using the MYRIGHTS command. This document defines two initial access calculation models: UNION and MOST-SPECIFIC. If a server implementing ACL2 uses the union of the rights granted to the applicable identifiers minus the union of the negative rights in order to calculate access, it MUST report "ACL2=UNION" in the server's capability list. See also section 7.2.1. An implementation may instead choose to only use those rights granted to the most specific identifier present in the ACL. In this case the server MUST report "ACL2=MOST-SPECIFIC" in the server's capability list. See also section 7.2.2. If the server implements any other policy for rights calculation, it MUST be either registered with IANA using the template provided in 7.1 or start with "X-". The server MUST report one and only one "ACL2=<rule-ID>" capability in its CAPABILITY response. 3.3. Rights required to perform different IMAP4rev1 commands Before executing a command an ACL2 compliant server must check which rights are required to perform it. This section groups command by functions they perform and list the rights required. It also gives the detailed description of any special processing required. Listing and subscribing/unsubscribing mailboxes: LIST - "l" right is required. Note, that if the user has "l" right to a mailbox "A/B", but not to its parent mailbox "A", the LIST command should behave as if the mailbox "A" doesn't exist, for example: C: A777 LIST "" * S: * LIST (\NoInferiors) "/" "A/B" S: * LIST () "/" "C" S: * LIST (\NoInferiors) "/" "C/D" S: A777 OK LIST completed SUBSCRIBE - "l" right is required only if the server checks for mailbox existence when performing SUBSCRIBE. UNSUBSCRIBE - no rights required to perform this operation. LSUB - "l" right is required only if the server checks for mailbox existence when performing SUBSCRIBE. Mailbox management: CREATE - "c" right on a nearest existing parent mailbox. When a new mailbox is created it SHOULD inherit rights from the parent mailbox (if one exists) in the defined hierarchy. DELETE - "x" right on the mailbox. RENAME - Moving a 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" to "D/E", the user must have "x" right for the mailbox "A/B/C" and "c" right for the mailbox "D". Copying or appending messages: Before performing a COPY/APPEND command the server MUST check if the user has "i" right for the target mailbox. If the user doesn't have "i" right, the operation fails. Otherwise for each copied/appended message the server MUST check if the user has "t" right - when the message has \Deleted flag set "s" right - when the message has \Seen flag set "w" right for all other message flags. Only when the user has a particular right the corresponding flags are stored for the newly created message. The server MUST NOT fail a COPY/APPEND if the user has no rights to set a particular flag. Example: C: A003 MYRIGHTS TargetMailbox S: * MYRIGHTS INBOX rwis S: A003 OK Myrights complete C: A004 FETCH 1:3 (FLAGS) S: * 1 FETCH (FLAGS (\Draft \Deleted) S: * 2 FETCH (FLAGS (\Answered) S: * 3 FETCH (FLAGS ($Forwarded \Seen) S: A004 OK Fetch Completed C: A005 COPY 1:3 TargetMailbox S: A005 OK Copy completed C: A006 SELECT TargetMailbox ... S: A006 Select Completed Let's assume that the copied messages received message numbers 77:79. C: A007 FETCH 77:79 (FLAGS) S: * 77 FETCH (FLAGS (\Draft) S: * 78 FETCH (FLAGS (\Answered) S: * 79 FETCH (FLAGS ($Forwarded \Seen) S: A007 OK Fetch Completed \Deleted flag was lost on COPY, as the user has no "t" right in the target mailbox. If the MYRIGHT command with the tag A003 would have returned: S: * MYRIGHTS INBOX rsti the response from the FETCH with the tag A007 would have been: C: A007 FETCH 77:79 (FLAGS) S: * 77 FETCH (FLAGS (\Deleted) S: * 78 FETCH (FLAGS () S: * 79 FETCH (FLAGS (\Seen) S: A007 OK Fetch Completed In the latter case \Answered, $Forwarded and \Draft flags were lost on COPY, as the user has no "w" right in the target mailbox. Expunging the selected mailbox: EXPUNGE - "e" right on the selected mailbox. CLOSE - "e" right on the selected mailbox. If the server is unable to expunge the mailbox because the user doesn't have the "e" right, the server MUST ignore expunge request, close the mailbox and return tagged OK response. Fetch information about a mailbox and its messages: SELECT/EXAMINE/STATUS - "r" right on the mailbox. FETCH - A FETCH request that implies setting \Seen flag MUST NOT set it, if the current user doesn't have "s" right. Changing flags: STORE - the server MUST check if the user has "t" right - when the user modifies \Deleted flag "s" right - when the user modifies \Seen flag "w" right for all other message flags. STORE operation SHOULD NOT fail if the user has rights to modify at least one flag specified in the STORE. Changing ACLs: ACL STORE/DELETE/SET - "a" right on the mailbox (*). Reading ACLs: ACL GET - "a" right on the mailbox (*). MYRIGHTS - any of the following rights is required to perform the operation: "l", "r", "i", "c", "x", "e", "a". (*) Note, that when one or more mailbox pattern is specified, 'l' right is required for each mailbox matching the mailbox pattern(s). 4. ACL manipulation commands All ACL commands (i.e. ACL STORE/DELETE/SET/GET, except for MYRIGHTS) accept either a single mailbox name or several mailbox patterns as a parameter. Mailbox pattern is a mailbox with wildcards, wildcards are interpreted as described in [IMAP4] LIST command. In order to distinguish between a mailbox name (that is allowed to have wildcard characters '*' and '%') and a mailbox pattern, the latter is always represented as a parenthesized list. For simplicity the behaviour of ACL STORE/DELETE/SET/GET commands is described for a single mailbox case. When one or more mailbox pattern is specified, the server internally performs LIST command for all specified patterns and than it combines the results. Note, that only mailboxes for which the user has 'l' right are included in the combined result. If the combined result has no mailboxes, an ACL operation completes with success and the tagged OK response is sent. Otherwise the requested operation is performed for each mailbox in the combined result. If a particular mailbox causes the operation to fail (e.g. insufficient permissions), instead of failing the whole command, an untagged ACLFAILED or RIGHTS-INFO response is sent for this mailbox and the operation continues for the rest of the mailboxes. If the server knows that the operation will fail in the same manner for all matching mailboxes (e.g. user doesn't exist), it SHOULD return tagged NO response instead of sending several untagged ACLFAILED responses. Example: In the example below ACL SET command fails for 2 mailboxes "Personal/Jokes" and "Personal/Deaf and Blind". For the latter a human readable error description is returned. Also, the ACL for the mailbox "Personal/Secret" was updated to include the "r" right for a user "user=Boss" as a side effect of the ACL SET command (see also 4.3). C: A002 ACL SET (INBOX Personal/*) user=Fred rwist S: * ACLFAILED Personal/Jokes S: * ACLFAILED "Personal/Deaf and Blind" Temporary Error S: * LIST () "/" Personal/Secret (("ACL" (("user=Boss" "r")))) S: A002 OK acl set completed Example: C: A002 ACL SET (Fruits/Apples/*) user=Zak lrs S: A002 NO User Zak doesn't exist 4.1. ACL STORE Arguments: mailbox name or one or more mailbox masks authentication identifier access right modification Data: OPTIONAL untagged responses: LIST with ACL information (see 5.1) Result: OK - ACL STORE completed NO - ACL STORE failure: can't set acl BAD - command unknown or arguments invalid The ACL STORE 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. Note, that for "ACL2=UNION" access calculation rule <ACL STORE mailbox identifier ""> MUST be treated as <ACL DELETE mailbox identifier>. Also note that these two commands don't have the same result for "ACL2=MOST-SPECIFIC". An ACL2 server MAY modify one or more ACL for one or more identifier as a side effect of modifying the ACL specified in ACL STORE. If the server does that it MUST send untagged LIST response with ACL information (see section 5.1) to notify the client about the changes made. If the server is unwilling to perform the command, because some rights for the identifier are tied, it MUST return RIGHTS-INFO untagged response (see section 5.2). Example: C: A002 ACL STORE ~/Mail/saved user=smith cp S: * RIGHTS-INFO ~/Mail/saved user=smith la r swi cdext p S: A002 NO Acl store failed, some rights are tied Client decides to grant both rights to the identifier: C: A003 ACL STORE ~/Mail/saved smith cdextp S: A003 OK Setacl complete 4.2. ACL DELETE Arguments: mailbox name or one or more mailbox masks authentication identifier Data: OPTIONAL untagged responses: LIST with ACL information (see 5.1) Result: OK - ACL DELETE completed NO - ACL DELETE failure: can't delete acl BAD - command unknown or arguments invalid The ACL DELETE command removes any <identifier,rights> pair for the specified identifier from the access control list for the specified mailbox. An ACL2 server MAY modify one or more ACL for one or more identifier as a side effect of modifying the ACL specified in ACL DELETE. If the server does that it MUST send untagged LIST response with ACL information (see section 5.1) to notify the client about the changes made. 4.3. ACL SET Arguments: mailbox name or one or more mailbox masks list of (authentication identifier, access rights) pairs Data: OPTIONAL untagged responses: LIST with ACL information (see 5.1) Result: OK - replaceacl completed NO - replaceacl failure: can't replace acl BAD - command unknown or arguments invalid The ACL SET command replaces the access control list of the specified mailbox with the one provided as the second parameter to ACL SET. This command is semantically equivalent to the following sequence of commands: 1). ACL GET <mailbox name> 2). For each (authentication identifier AID, access rights RD) pair returned in the untagged ACL response that was caused by ACL GET, perform ACL DELETE <mailbox name> AID 3). For each (authentication identifier AIA, access rights RA) pair from the second parameter of ACL SET perform ACL STORE <mailbox name> AIA RA An ACL2 server MAY modify one or more ACL for one or more identifier as a side effect of modifying the ACL specified in ACL SET. If the server does that it MUST send untagged LIST response with ACL information (see section 5.1) to notify the client about the changes made. If the server is unwilling to perform the command, because some rights for an identifier from the second list parameter are tied, it MUST return RIGHTS-INFO untagged response (see section 5.2). 4.4. ACL GET Arguments: mailbox name or one or more mailbox masks Data: REQUIRED untagged responses: LIST with ACL information (see 5.1) Result: OK - ACL GET completed NO - ACL GET failure: can't get acl BAD - command unknown or arguments invalid The ACL GET command returns the access control list for mailbox in an untagged LIST response (see section 5.1). Example: C: A002 ACL GET INBOX S: * LIST () "/" INBOX (("ACL" (("user=Fred" "rwipslextda")))) S: A002 OK acl get complete 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. The user must have any of the following rights to perform this operation: "l", "r", "i", "c", "x", "e", "a". If the user doesn't have any right from the above list, the server MUST behave as if the mailbox doesn't exist. Example: C: A003 MYRIGHTS INBOX S: * MYRIGHTS INBOX rwipsldexta S: A003 OK Myrights complete 5. ACL related responses 5.1. Extended LIST response with ACL information Contents: name attributes hierarchy delimiter mailbox name ACL information (zero or more identifier rights pairs) This version of LIST response occurs as a result of an ACL GET command. It MAY also occur as a result of ACL STORE/DELETE/SET. The proposed syntax conforms to the syntax of an extended LIST response as defined by mbox-list-extended ABNF element of [LISTEXT]. The meaning of "name attributes" and "hierarchy delimiter" is described in section 7.2.2 of [IMAP4]. Hierarchy delimiter is followed by a mailbox name for which this ACL applies. This is followed by extention part that includes "ACL" tag 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. <<Name attributes doesn't have to be precise for the purpose of this extention?>> <<Do we need "ACL" option to the LIST command?>> Example: S: * LIST () "/" INBOX (("ACL" (("user=Fred" "rwipslextda")))) The example above shows that a user Fred is granted "rwipslextda" rights to the mailbox "INBOX". S: * LIST () ":" Drafts (("ACL" (("user=Fred" "rwipslextda") ("group=Devel" "r")))) The example above shows that a user Fred is granted "rwipslextda" rights and a member of a group "Devel" is granted "r" right to the mailbox "Drafts". S: * LIST () NIL Manson (("ACL" ())) The example above shows the mailbox "Manson" has an empty ACL. 5.2. RIGHTS-INFO Data: mailbox name identifier required rights list of optional rights The RIGHTS-INFO response occurs as a result of a failed ACL STORE or ACL SET 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 RIGHTS-INFO response. 5.3. ACLFAILED untagged response Contents: mailbox name OPTIONAL response code and human readable text for failure reason The ACLFAILED response containing a mailbox name indicates that the ACL operations failed for the specified mailbox. The reason for failure may be described by the response code (if included). If the command for the mailbox fails because some rights are tied, the server MUST return RIGHTS-INFO response instead of ACLFAILED. Example: C: A002 ACL SET (INBOX Personal/*) user=Fred rwist S: * ACLFAILED Personal/ABC S: A002 OK acl set complete 5.4. MYRIGHTS untagged response 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. 5.5. MYRIGHTS response code Data: rights The MYRIGHTS response code is sent in an untagged OK response that results from SELECT/EXAMINE. Also this response code can be sent at any time after opening a mailbox when the server detects that the set of rights allowed for the logged in user has changed. The MYRIGHT response code is equivalent to MYRIGHTS untagged response for the selected mailbox. 6. Formal Syntax Formal syntax is defined using ABNF [ABNF] 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. acl2_command = myrights | "ACL" SP acl2_subcommand acl2_subcommand = replaceacl | deleteacl | updateacl | getacl | listrights acl_list_data = "(" acl_list_tag SP acl_data ")" ;; acl_list_data conforms to the syntax of ;; mbox-list-extended-item from [LISTEXT] acl_list_tag = <"> "ACL" <"> ace = "(" identifier SP rights ")" acl_data = "(" [ace *( SP ace )] ")" ;; zero or more parenthesized identifier/rights pairs <<Currently the empty list doesn't conform to mbox-list-extended-item syntax!>> always_granted = rights deleteacl = "DELETE" SP mbox_or_pat SP identifier getacl = "GET" SP mbox_or_pat identifier = astring ;; UTF-8 string with syntax of ident_syntax ident_syntax = ident | "-" ident ident = ident_special | ident_user | ident_group | ident_vendor ident_special = "anyone" | "authuser" | "owner" | "administrators" ident_user = "user=" ident_detail ident_group = "group=" ident_detail ident_vendor = "vendor=" ident_vname "." ident_detail ident_detail = 1*UTF8-CHAR ident_vname = 1*UTF8-CHAR ;; MUST NOT contain "." listrights = "LIST" SP mbox_or_pat SP identifier listrights_data = "RIGHTS-INFO" SP mailbox SP identifier SP always_granted *(SP rights) mod_rights = quoted ;; +rights to add, -rights to remove myrights = "MYRIGHTS" SP mailbox myrights_data = "MYRIGHTS" SP mailbox SP rights myrights_rspcod = "MYRIGHTS" SP rights replaceacl = "SET" SP mbox_or_pat *(SP identifier SP rights) resp-text-code =/ myrights_data rights = quoted ;; MUST NOT contain leading "+" or "-" updateacl = "STORE" SP mbox_or_pat SP identifier SP mod_rights mbox_or_pat = mailbox / patterns patterns = "(" list-mailbox *(list-mailbox) ")" partialfail_rsp = "ACLFAILED" SP mailbox [SP ["[" resp-text-code "]" SP] text] ;; May contain optional failure reason followed by a ;; human readable text UTF8-CHAR = CHAR | UTF8-2 | UTF8-3 | UTF8-4 | UTF8-5 | UTF8-6 CHAR = %x01-7F UTF8-loworder = %x80-BF UTF8-2 = %xC1-DF UTF8-loworder ;; Disallow overlong sequences beginning with 0xC0. UTF8-3 = (%xE0 %xA0-BF UTF8-loworder) | (%xE1-EC 2UTF8-loworder) | (%xED %x80-9F UTF8-loworder) | (%xEE 2UTF8-loworder) | (%xEF %x80-BE UTF8-loworder) | (%xEF %xBF %x80-BD) ;; Disallow overlong sequences beginning with 0xE0, ;; disallow encoded surrogate characters, and ;; disallow U+FFFE, U+FFFF. UTF8-4 = (%xF0 %x90-BF 2UTF8-loworder) | (%xF1-F7 3UTF8-loworder) ;; Disallow overlong sequences beginning with 0xF0. UTF8-5 = %xF8-FB 4UTF8-1 UTF8-6 = %xFC-FD 5UTF8-1 7. IANA considerations 7.1. ACL access calculation rule Registration Template When an access calculation rule for ACL2 extension is registered, the following information is supplied: Rule Identification: specify a string that identifies this rule. Unless the rule is registered with the IANA, the rule's identification must start with "X-". The server supporting a particular rule <rule-ID> MUST report "ACL2=<rule-ID>" in the capability list. Rule Semantics: specify how access rights for a mailbox are calculated. Negative rights allowed: specify whether "negative right" identifiers are allowed. Groups allowed: specify whether group identifiers are allowed. Special Identifiers: describe whether any implementation defined aliases are allowed and define their meaning. Contact Information: specify the postal and electronic contact information for the author of the feature. 7.2. Initial Registrations 7.2.1. Registration: UNION access calculation rule Rule Identification: UNION Rule Semantics: the union of the rights granted to the applicable identifiers minus the union of the negative rights. Negative rights allowed: Yes. Groups allowed: Yes, but not required. Special Identifiers: No. Contact Information: c.f., the "Editor's Address" section of this memo 7.2.2. Registration: MOST-SPECIFIC access calculation rule Rule Identification: MOST-SPECIFIC Rule Semantics: the rights granted to the most specific identifier present in the ACL are used, i.e. if the user identifier is present, its ACL is used. If no user identifier is present, but a group that includes this user as a member is present, the group ACL is used. If neither user, nor group identifier is present, but an ACL for a special group "anyone" is present, the ACL for "anyone" is used. Negative rights allowed: No. Groups allowed: Yes, but not required. Special Identifiers: No. Contact Information: c.f., the "Editor's Address" section of this memo 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 ACL GET command on a mailbox for which the user has insufficient rights should not admit the mailbox exists, much less return the mailbox's ACL. IMAP clients implementing ACL2 that are able to modify ACLs SHOULD warn a user that wants to give full access (or even just "a" right) to the special identifier "anyone". 9. Other considerations 9.1. Compatibility with RFC 2086 This section gives guidelines how an existing RFC 2086 implementation may be modified to support ACL2. 1). Special handling of new identifiers. Two approaches: a). prohibit the creation of users on the mail system with special names (ident_special token in the ABNF) and prohibit to use "=" in identifier names. Treat "user=<identif>" the same way as "<identif>" in both ACL and ACL2 version of commands. b). implement translation from "user=<identif>" to "<identif>" internally. 2). "d" right mapping to "x", "t" and "e" and back. Two approaches: a). Tie "x", "t" and "e" together - almost no changes b). Implement separate "x", "t" and "e". Return "d" right in a LIST response containing ACL information when all three of "x", "t" and "e" are granted. 3). "rights" can be only sent as quoted strings, not as literals. 4). Send untagged LIST response with ACL information when server changes other ACLs on ACL STORE/DELETE/SET (servers that don't do that don't have to care). Additional work required to implement ACL2 when RFC 2086 is already implemented: 1). Recognize new command names 2). Handle multiple mailboxes (a la LIST), return ACLFAILED on a failure. 3). Implement ACL SET 4). Optional: send MYRIGHTS untagged response on SELECT/EXAMINE 5). LISTRIGHTS command is deprecated. LISTRIGHTS response is replaced with RIGHTS-INFO response code. 6). Report "ACL2=UNION" capability. 7). Implement new special identifiers or groups if desired. 9.2. ACL2 interaction with QUOTA extension Server that implement both ACL2 and QUOTA extensions MUST use the following table to determine if a quota operation should be allowed for the user: GETQUOTAROOT - any of the following rights is required to perform the operation: "r", "i", "a". <<"r" allows to calculate usage, "i" allows to put a mailbox overquota and get mailbox usage with certain implementations, that check message size before receiving the message in APPEND>> GETQUOTA - no rights required SETQUOTA - implementation defined, as SETQUOTA operates on a quotaroot, not on a mailbox. 9.3. Mapping of ACL rights to READ-WRITE and READ-ONLY response codes A particular ACL2 server implementation may allow "shared multiuser access" to some mailboxes. "Shared multiuser access" to a mailbox means that multiple different users are able to access the same mailbox, if they have proper access rights. "Shared multiuser access" to the mailbox doesn't mean that the ACL for the mailbox is currently set to allow access by multiple users. Let's denote a "shared multiuser write access" as a "shared multiuser access" when a user may be granted flag modification rights (any of "w", "s" or "t"). Section 3.3 ("Rights required to perform different IMAP4rev1 commands") describes which rights are required for modifying different flags. If the ACL2 server implements some flags as shared for a mailbox (i.e., the ACL for the mailbox may be set up so that changes to those flags are visible to another user), let's call the set of rights associated with these flags (as described in 3.3) for that mailbox collectively as "shared flag rights". Note, that "shared flag rights" set MAY be different for different mailboxes. If the server doesn't support "shared multiuser write access" to a mailbox or doesn't implement shared flags on the mailbox, "shared flag rights" for the mailbox is defined to be the empty set. Example 1: Mailbox "banan" allows "shared multiuser write access" and implements flags \Deleted, \Answered and $MDNSent as shared flags. "Shared flag rights" for the mailbox "banan" is a set containing flags "t" (because system flag \Deleted requires "t" right) and "w" (because both \Answered and $MDNSent require "w" right). Example 2: Mailbox "apple" allows "shared multiuser write access" and implements \Seen system flag as shared flag. "Shared flag rights" for the mailbox "apple" contains "s" right, because system flag \Seen requires "s" right. Example 3: Mailbox "pear" allows "shared multiuser write access" and implements flags \Seen, \Draft as shared flags. "Shared flag rights" for the mailbox "apple" is a set containing flags "s" (because system flag \Seen requires "s" right) and "w" (because system flag \Draft requires "w" right). The server MUST include a READ-ONLY prefix in the tagged OK response to a SELECT command if none of the following rights is granted to the current user: "i", "e" and "shared flag rights". The server SHOULD include a READ-WRITE prefix in the tagged OK response if at least one of the "i", "e" or "shared flag rights" is granted to the current user. Example 1 (continue): The user that has "lrs" rights for the mailbox "banan". The server returns READ-ONLY response code on SELECT, as none of "iewt" rights is granted to the user. Example 2 (continue): The user that has "rit" rights for the mailbox "apple". The server returns READ-WRITE response code on SELECT, as the user has "i" right. Example 3 (continue): The user that has "rset" rights for the mailbox "pear". The server returns READ-WRITE response code on SELECT, as the user has "e" and "s" rights. 9.4. Additional requirements and Implementation notes Any server implementing an ACL2 extension MUST accurately reflect the current user's rights in FLAGS and PERMANENTFLAGS responses. The server SHOULD issue a MYRIGHTS response code in an untagged OK response as a result of a SELECT or EXAMINE command. Example: C: A142 SELECT INBOX S: * 172 EXISTS S: * 1 RECENT S: * OK [UNSEEN 12] Message 12 is first unseen S: * OK [UIDVALIDITY 3857529045] UIDs valid S: * OK [UIDNEXT 4392] Predicted next UID S: * FLAGS (\Answered \Flagged \Deleted \Seen \Draft) S: * OK [PERMANENTFLAGS (\Deleted \Seen \*)] Limited S: * OK [MYRIGHTS rwiste] Allowed rights S: A142 OK [READ-WRITE] SELECT completed An ACL2 server MAY modify one or more ACL for one or more identifier as a side effect of modifying the ACL specified in ACL STORE/DELETE/SET. If the server does that it MUST send untagged ACL response to notify the client about the changes made. 10. Normative References [KEYWORDS] Bradner, "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, Harvard University, March 1997. [ABNF] Crocker, Overell, "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, Internet Mail Consortium, Demon Internet Ltd, November 1997. [IMAP4] Crispin, M., "Internet Message Access Protocol - Version 4rev1", RFC 2060, University of Washington, December 1996. [UTF-8] Yergeau, F., "UTF-8, a transformation format of IS0 10646", RFC 2279, Alis Technologies, January 1998. [QUOTA] Myers, J., "IMAP4 QUOTA extension", RFC 2087, Carnegie Mellon University, January 1997. 11. Informative References [LISTEXT] Leiba, B., "IMAP4 LIST Command Extensions", work in progress, draft-ietf-imapext-list-extensions-02.txt, IBM T.J. Watson Research Center. 12. Aknowledgement This document is a revision of the RFC 2086 written by John G. Myers. Editor appreciates comments received from Mark Crispin, Chris Newman, Cyrus Daboo, John G. Myers, Steve Hole, Curtis King, Lyndon Nerenberg, Larry Greenfield, Vladimir Butenko, Dave Cridland, Harrie Hazewinkel and other participants of IMAPEXT working group. 13. Editor's Address Alexey Melnikov mailto: mel@messagingdirect.com ACI WorldWide/MessagingDirect 59 Clarendon Road, Watford, Hertfordshire, United Kingdom, WD17 1FQ Phone: +44 1923 81 2877 14. Full Copyright Statement Copyright (C) The Internet Society 2003. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Appendix A. Changes since RFC 2086 1. Changed the charset of "identifier" from US-ASCII to UTF-8. 2. Changed identifier syntax. Now all users must start with "user=" prefix. Specified that identifiers starting with a "group=" prefix are reserved for groups and implementation defined aliases. 3. Specified that mailbox deletion is controled by the "x" right and EXPUNGE is controlled by "e" right. 4. Clarified that RENAME requires "c" right for the new parent and "x" right for the old name. 5. Changed capability name from "ACL" to "ACL2" because changes 2 and 3 are not backward compatible with ACL RFC. 6. Added "t" right that controls STORE \Deleted. Redefined "d" to be a macro for "e", "x" and "t". 7. Added "ACL2=UNION" and "ACL2=MOST-SPECIFIC" capabilities and IANA registration template. 8. Specified that "a" right also controls DELETEACL 9. Specified that "r" right also controls STATUS 10. Specified that "w" controls setting flags other than \Seen and \Deleted on APPEND. Same for "s" and "t" flags. 11. Specified that "l" controls SUBSCRIBE/UNSUBSCRIBE. 12. Added "Compatibility with RFC 2086" section. 13. Added "Implementation Notes" section. 14. Updated "References" section. 15. Deleted "PARTIAL", this is a deprecated feature of RFC1730. 16. Added MYRIGHT response code as per Cyrus suggestion. 17. Added REPLACEACL (ACL SET) as per Mark and Cyrus request. 18. Added new section that describes which rights are required and/or checked when performing various IMAP commands. 19. Added section about interaction of ACL2 with the QUOTA extension. 20. Added special identifiers "authuser", "owner" and "administrators". 21. Added mail client security considerations when dealing with special identifier "anyone". 22. Clarified that negative rights are not the same as DELETEACL (ACL DELETE). 23. Removed the requirement to check the "r" right for CHECK, SEARCH and FETCH, as this is required for SELECT/EXAMINE to be successful. 24. Added note that a server can modify an ACL for any identifier(s) as a side effect of performing SETACL/DELETEACL/REPLACEACL (ACL STORE/DELETE/SET). Also specified that the server MUST send untagged ACL response if it does that. Updated command definition to include optional ACL untagged response. 25. Fixed typo in 10.1. (Was "ACL=...", not "ACL2=...") 26. Cleaned up section 10.2 a bit. 27. LISTRIGHTS (ACL LIST) requires same rights as MYRIGHTS. 28. Added section about mapping of ACL rights to READ-WRITE and READ-ONLY response codes. 29. Changed ABNF for rigths/mod_rights to be quoted instead of astring. 30. Changed syntax of ACL2 commands according to the following table: SETACL => ACL STORE DELETEACL => ACL DELETE REPLACEACL => ACL SET GETACL => ACL GET LISTRIGHTS => ACL LIST MYRIGHTS was left as is Changed syntax of ACL2 responses: ACL => Extended LIST response with ACL information LISTRIGHTS => RIGHTS-INFO MYRIGHTS was left as is Any better suggestions for names are welcome. 31. Added mailbox patterns and partial failures. Updated ABNF. 32. SUBSCRIBE is NOT allowed with "r" right. 33. GETACL (ACL GET) is NOT allowed with "r" right. 34. Added human readable text to ACLFAILED untagged response. 35. GETQUOTAROOT requires any one of "r", "i" or "a". 36. Removed ACL LIST (LISTRIGHTS) command. 37. Added "vendor=" identifier prefix for vendor specific identifiers. 38. Added ABNF for identifier syntax. 39. Text and document structure change based on comments from Harrie Hazewinkel. 40. Replaced "ACLINFO" response with a special variant of LIST. Updated text and ABNF. 41. Replaced SPACE with SP in the ABNF section.
Datatracker
draft-ietf-imapext-acl-07
Internet-Draft
