One document matched: draft-ietf-imapext-acl-08.txt
Differences from draft-ietf-imapext-acl-07.txt
IMAPEXT Working Group A. Melnikov
Internet Draft Editor
Document: draft-ietf-imapext-acl-08.txt June 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). Cleanup appendix A before publication as RFC, as some changes don't
apply to RFC 2086.
7). 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 LIST with the ACL parameter .............................. X
4.5 LIST with the MYRIGHTS parameter ......................... 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 Extended LIST response with MYRIGHTS information ......... 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.
Also note, that this document doesn't define how groups and administrators
are managed.
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. The format of the submission address
is not defined by this document)
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
a LIST (ACL) 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 LIST (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.
The table below summarizes different rights or their combinations that are
required in order to perform different IMAP operations. As it is not always
possible to express complex right checking and interactions, the description
after the table should be used as the primary reference.
+---------------------+---+---+---+---+---+---+---+---+---+---+-----+------+
| Operations\Rights | l | r | s | w | i | c | x | t | e | a | Any | None |
+---------------------+---+---+---+---+---+---+---+---+---+---+-----+------+
| LIST | + | | | | | | | | | | | |
| SUBSCRIBE | * | | | | | | | | | | | * |
| UNSUBSCRIBE | | | | | | | | | | | | + |
| LSUB | * | | | | | | | | | | | * |
| CREATE (for parent) | | | | | | + | | | | | | |
| DELETE | | | | | | | + | | | | | |
| RENAME | | | | | | + | + | | | | | |
| COPY/APPEND | | | ? | ? | + | | | ? | | | | |
| EXPUNGE/CLOSE | | | | | | | | | + | | | |
|SELECT/EXAMINE/STATUS| | | | | | | | | | | | |
| FETCH | | | ? | | | | | | | | | |
| STORE flags | | | ? | ? | | | | ? | | | | |
|ACL STORE/DELETE/SET | ? | | | | | | | | | + | | |
| LIST (ACL) | ? | | | | | | | | | + | | |
| LIST (MYRIGHTS)| | | | | | | | | | | + | |
+---------------------+---+---+---+---+---+---+---+---+---+---+-----+------+
Legend:
+ - The right is required
* - Only one of the rights marked with * is required (see description below)
? - The right is optional (see description below)
"Any" - at least one of the "l", "r", "i", "c", "x", "e", "a" rights is
required
"None" - No rights required to perform the command
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 LIST (MYRIGHTS) "" TargetMailbox
S: * LIST () "/" TargetMailbox (("MYRIGHTS" "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 LIST (MYRIGHT) command with the tag A003 would have returned:
S: * LIST () "/" TargetMailbox (("MYRIGHTS" "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:
LIST (ACL) - "a" right on the mailbox (*).
LIST (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)
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 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). LIST (ACL) "" <mailbox name>
2). For each (authentication identifier AID, access rights RD) pair returned
in the untagged LIST response that was caused by LIST (ACL), 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. LIST with the ACL parameter
This document defines a new option ACL to the LIST command that requests
the server to return the corresponding ACLs for all mailboxes that
match the LIST mailbox name. The ACL option causes the server
to return LIST with the ACL information (see 5.1).
<<List required rights here?>>
Example: C: A002 LIST (ACL) "" INBOX
S: * LIST () "/" INBOX (("ACL" (("user=Fred" "rwipslextda"))))
S: A002 OK List with acl info completed
4.5. LIST with the MYRIGHTS parameter
This document defines a new option MYRIGHTS to the LIST command that requests
the server to return the set of rights that the user has to a mailbox,
that matches the LIST mailbox name. The MYRIGHTS option causes the server
to return LIST with MYRIGHTS information (see 5.4).
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: A002 LIST (MYRIGHTS) "" INBOX
S: * LIST () "/" INBOX (("MYRIGHTS" "rwipsldexta"))
S: A002 OK List with acl info completed
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 LIST (ACL) 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 which this ACL applies to. This is followed by the extension part that
includes "ACL" tag followed by zero or more pairs of strings, each pair
contains the identifier followed by the set of rights that the identifier has.
<<Name attributes doesn't have to be precise for the purpose of this extension?>>
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. Extended LIST response with MYRIGHTS information
Contents: name attributes
hierarchy delimiter
mailbox name
MYRIGHTS information (list of rights)
This version of LIST response occurs as a result of a LIST (MYRIGHTS)
command. 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]. This is followed by the extension part that
includes "MYRIGHTS" tag followed by the set of rights that the user has.
<<Should this be simplified so that we don't repeat general LIST[EXT] stuff?>>
Example: S: * LIST () "/" Sent (("MYRIGHTS" "lrwiste"))
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 MYRIGHTS response code is equivalent to the MYRIGHTS data returned
in an untagged LIST 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] or [LISTEXT].
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 = "ACL" SP acl2_subcommand | list
acl2_subcommand = replaceacl | deleteacl | updateacl
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
option =/ "ACL" | "MYRIGHTS"
;; <option> is defined in [LISTEXT]
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_data = "RIGHTS-INFO" SP mailbox SP identifier
SP always_granted *(SP rights)
mod_rights = quoted
;; +rights to add, -rights to remove
myrights_list_data
= "(" "MYRIGHTS" SP rights ")"
;; myrights_list_data conforms to the syntax of
;; mbox-list-extended-item from [LISTEXT]
myrights_rspcod = "MYRIGHTS" SP rights
replaceacl = "SET" SP mbox_or_pat *(SP identifier SP rights)
resp-text-code =/ myrights_rspcod
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 electronic (and optionally postal) 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 LIST (ACL) 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 3501, University of Washington, March 2003.
[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@isode.com
Isode Limited
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 => LIST (ACL)
LISTRIGHTS => ACL LIST
MYRIGHTS => LIST (MYRIGHTS)
Changed syntax of ACL2 responses:
ACL => Extended LIST response with ACL information
LISTRIGHTS => RIGHTS-INFO
MYRIGHTS => Extended LIST response with MYRIGHTS information
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 ("LIST (ACL)") 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.
42. Added notes that group and administrators management, as well as
the format of an email for posting to a mailbox is out of scope.
43. Added a table that describes all operations and right required to
perform them.
44. Fixed several MYRIGHTS examples.
45. Updated ABNF to reflect recent changes ("MYRIGHTS" to "LIST (MYRIGHTS)"
and "ACL GET" to "LIST (ACL)")
| PAFTECH AB 2003-2026 | 2026-04-24 01:30:07 |