INTERNET-DRAFT Geoffrey Clemm, Rational Software
draft-ietf-webdav-acl-06 Anne Hopkins, Microsoft Corporation
Eric Sedlar, Oracle Corporation
Jim Whitehead, U.C. Santa Cruz
Expires December 21, 2001 June 21, 2001
WebDAV Access Control Protocol
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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-
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Internet-Drafts are draft documents valid for a maximum of six
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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
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Abstract
This document specifies a set of methods, headers, and message
bodies that define Access Control extensions to the WebDAV
Distributed Authoring Protocol. This protocol permits a client to
remotely read and modify access control lists that instruct a server
whether to grant or deny operations upon a resource (such as HTTP
method invocations) by a given principal.
This document is a product of the Web Distributed Authoring and
Versioning (WebDAV) working group of the Internet Engineering Task
Force. Comments on this draft are welcomed, and should be addressed
to the acl@webdav.org mailing list. Other related documents can be
found at http://www.webdav.org/acl/, and
http://www.ics.uci.edu/pub/ietf/webdav/.
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Table of Contents
1 INTRODUCTION...................................................4
1.1 Terms.......................................................5
1.2 Notational Conventions......................................6
2 PRINCIPALS.....................................................6
3 PRIVILEGES.....................................................7
3.1 DAV:read Privilege..........................................8
3.2 DAV:write Privilege.........................................8
3.3 DAV:read-acl Privilege......................................9
3.4 DAV:read-current-user-privilege-set Privilege...............9
3.5 DAV:write-acl Privilege.....................................9
3.6 DAV:all Privilege...........................................9
3.7 Aggregation of Predefined Privileges........................9
4 PRINCIPAL PROPERTIES..........................................10
4.1 DAV:alternate-URL..........................................10
5 ACCESS CONTROL PROPERTIES.....................................10
5.1 DAV:owner..................................................11
5.1.1 Example: Retrieving DAV:owner............................11
5.1.2 Example: An Attempt to Set DAV:owner.....................12
5.2 DAV:supported-privilege-set................................13
5.2.1 Example: Retrieving a List of Privileges Supported on a
Resource.................................................14
5.3 DAV:current-user-privilege-set.............................15
5.3.1 Example: Retrieving the User's Current Set of Assigned
Privileges...............................................16
5.4 DAV:acl....................................................17
5.4.1 ACE Principal............................................17
5.4.2 ACE Grant and Deny.......................................18
5.4.3 ACE Protection...........................................18
5.4.4 ACE Inheritance..........................................18
5.4.5 Example: Retrieving a Resource's Access Control List.....19
5.5 DAV:acl-semantics..........................................20
5.5.1 Example: Retrieving DAV:acl-semantics....................21
5.6 DAV:principal-collection-set...............................22
5.6.1 Example: Retrieving DAV:principal-collection-set.........22
5.7 Example: PROPFIND to retrieve access control properties....23
6 ACL SEMANTICS.................................................27
6.1 ACE Combination............................................27
6.1.1 DAV:first-match ACE Combination..........................27
6.1.2 DAV:all-grant-before-any-deny ACE Combination............27
6.1.3 DAV:specific-deny-overrides-grant ACE Combination........27
6.2 ACE Ordering...............................................28
6.2.1 DAV:deny-before-grant ACE Ordering.......................28
6.3 Allowed ACE................................................28
6.3.1 DAV:principal-only-one-ace ACE Constraint................28
6.3.2 DAV:grant-only ACE Constraint............................28
6.4 Required Principals........................................28
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7 ACCESS CONTROL AND EXISTING METHODS...........................29
7.1 OPTIONS....................................................29
7.1.1 Example - OPTIONS........................................29
7.2 MOVE.......................................................29
7.3 COPY.......................................................29
8 ACCESS CONTROL METHODS........................................29
8.1 ACL........................................................29
8.1.1 ACL Preconditions........................................30
8.1.2 Example: the ACL method..................................31
8.1.3 Example: ACL method failure due to protected ACE
conflict ................................................32
8.1.4 Example: ACL method failure due to an inherited ACE
conflict ................................................33
8.1.5 Example: ACL method failure due to an attempt to set
grant and deny in a single ACE ..........................34
9 ACCESS CONTROL REPORTS........................................35
9.1 REPORT Method..............................................35
9.2 DAV:acl-principal-props Report.............................36
9.2.1 Example: DAV:acl-principal-props Report..................36
9.3 DAV:principal-match REPORT.................................37
9.3.1 Example: DAV:principal-match REPORT......................38
10 XML PROCESSING..............................................39
11 INTERNATIONALIZATION CONSIDERATIONS.........................39
12 SECURITY CONSIDERATIONS.....................................40
12.1 Increased Risk of Compromised Users........................40
12.2 Risks of the DAV:read-acl and DAV:current-user-privilege-set
Privileges.................................................40
12.3 No Foreknowledge of Initial ACL............................41
13 AUTHENTICATION..............................................41
14 IANA CONSIDERATIONS.........................................42
15 INTELLECTUAL PROPERTY.......................................42
16 ACKNOWLEDGEMENTS............................................42
17 REFERENCES..................................................43
17.1 Normative References.......................................43
17.2 Informational References...................................43
18 AUTHORS' ADDRESSES..........................................43
19 APPENDICIES.................................................44
19.1 XML Document Type Definition...............................44
20 NOTE TO RFC EDITOR..........................................46
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1 INTRODUCTION
The goal of the WebDAV access control extensions is to provide
an interoperable mechanism for handling discretionary access
control for content in WebDAV servers. WebDAV access control
can be implemented on content repositories with security as
simple as that of a UNIX file system, as well as more
sophisticated models. The underlying principle of access
control is that who you are determines how you can access a
resource. The "who you are" is defined by a "principal"
identifier; users, client software, servers, and groups of the
previous have principal identifiers. The "how" is determined by
a single "access control list" (ACL) associated with a
resource. An ACL contains a set of "access control entries"
(ACEs), where each ACE specifies a principal and a set of
privileges that are either granted or denied to that principal.
When a principal submits an operation (such as an HTTP or
WebDAV method) to a resource for execution, the server
evaluates the ACEs in the ACL to determine if the principal has
permission for that operation.
This specification intentionally omits discussion of
authentication, as the HTTP protocol already has a number of
authentication mechanisms [RFC2617]. Some authentication
mechanism (such as HTTP Digest Authentication, which all WebDAV
compliant implementations are required to support) must be
available to validate the identity of a principal.
The following issues are out of scope for this document:
* Access control that applies only to a particular property
on a resource (excepting the access control properties
DAV:acl and DAV:current-user-privilege-set), rather than
the entire resource,
* Role-based security (where a role can be seen as a
dynamically defined collection of principals),
* Specification of the ways an ACL on a resource is
initialized,
* Specification of an ACL that applies globally to all
resources , rather than to a particular resource.
* Creation and maintenance of resources representing people
or computational agents (principals), and groups of these.
This specification is organized as follows. Section 1.1 defines
key concepts used throughout the specification, and is followed
by more in-depth discussion of principals (Section 2), and
privileges (Section 3). Properties defined on principals are
specified in Section 4, and access control properties for
content resources are specified in Section 5. The semantics of
access control lists are described in Section 6, including
sections on ACE combination (Section 6.1), ACE ordering
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(Section 6.2), and principals required to be present in an ACE
(Section 6.4). Client discovery of access control capability
using OPTIONS is described in Section 7.1, and the access
control setting method, ACL, is specified in Section 8.
Internationalization considerations (Section 11) and security
considerations (Section 12) round out the specification. An
appendix (Section 19.1) provides an XML Document Type
Definition (DTD) for the XML elements defined in the
specification.
1.1 Terms
This draft uses the terms defined in HTTP [RFC2616] and WebDAV
[RFC2518]. In addition, the following terms are defined:
principal
A "principal" is a distinct human or computational actor that
initiates access to network resources. In this protocol, a
principal is an HTTP resource that represents such an actor.
principal collection
A "principal collection" is a group of principals, and is
represented in this protocol by a WebDAV collection containing
HTTP resources that represent principals, and principal
collections.
privilege
A "privilege" controls access to a particular set of HTTP
operations on a resource.
aggregate privilege
An "aggregate privilege" is a privilege that contains a set of
other privileges.
abstract privilege
The modifier "abstract", when applied to a privilege, means the
privilege cannot be set in an access control element (ace).
access control list (ACL)
An "ACL" is a list of access control elements that define
access control to a particular resource.
access control element (ace)
An "ace" either grants or denies a particular set of (non-
abstract) privileges for a particular principal.
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inherited ace
An "inherited ace" is an ace that is dynamically shared from
the ACL of another resource. When a shared ACE changes on the
primary resource, it is also changed on inheriting resources.
protected property
A "protected property" is one whose value cannot be updated
except by a method explicitly defined as updating that specific
property. In particular, a protected property cannot be
updated with a PROPPATCH request.
1.2 Notational Conventions
The augmented BNF used by this document to describe protocol
elements is described in Section 2.1 of [RFC2616]. Because this
augmented BNF uses the basic production rules provided in
Section 2.2 of [RFC2616], those rules apply to this document as
well.
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 [RFC2119].
Definitions of XML elements in this document use XML element
type declarations (as found in XML Document Type Declarations),
described in Section 3.2 of [REC-XML].
2 PRINCIPALS
A principal is a network resource that represents a distinct
human or computational actor that initiates access to network
resources. On many implementations, users and groups are
represented as principals; other types of principals are also
possible. A URI of any scheme MAY be used to identify a
principal resource. However, servers implementing this
specification MUST expose principal resources at an http(s)
URL, which is a privileged scheme that points to resources that
have additional properties, as described in Section 4. So, a
principal resource can have multiple URI identifiers, one of
which has to be an http(s) scheme URL. Although an
implementation SHOULD support PROPFIND and MAY support
PROPPATCH to access and modify information about a principal,
it is not required to do so.
A principal resource may or may not be a collection. If a
person or computational agent matches a principal resource that
is contained by a collection principal, they also match the
collection principal. This definition is recursive, and hence
if a person or computational agent matches a collection
principal that is the child of another collection principal,
they also match the parent collection principal. Membership in
a collection principal is also recursive, so a principal in a
collection principal GRPA contained by collection principal
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GRPB is a member of both GRPA and GRPB. Implementations not
supporting recursive membership in principal collections can
return an error if the client attempts to bind collection
principals into other collection principals.
Servers that support aggregation of principals (e.g. groups of
users or other groups) MUST manifest them as collection
principals. At minimum, principals and collection principals
MUST support the OPTIONS and PROPFIND methods.
Implementer's Note: Collection principals are first and
foremost WebDAV collections. Therefore they contain
resources as members. Since there is no requirement that all
members of a collection principal need be principals, it is
possible for a collection principal to have non-principals
as members. When enumerating the principals-only membership
of a collection principal, it is necessary to retrieve the
DAV:resourcetype property and check it for the DAV:principal
XML element (described in Section 4). If the DAV:principal
XML element is not present, the resource is not a principal
and may be ignored for the purposes of determining the
principals-only membership of the collection principal.
For example, the collection principal /FOO/ has two members,
Bar and Baz. Bar is a principal but Baz is not. Therefore
when determining which principals belong to the collection
principal /FOO/, a client would enumerate the membership
using PROPFIND while asking for the DAV:resourcetype
property, and see that only Bar has the DAV:principal XML
element. Therefore, only Bar is the only principal that is a
member of the collection principal /FOO/.
3 PRIVILEGES
Ability to perform a given method on a resource SHOULD be
controlled by one or more privileges. Authors of protocol
extensions that define new HTTP methods SHOULD specify which
privileges (by defining new privileges, or mapping to ones
below) are required to perform the method. A principal with no
privileges to a resource SHOULD be denied any HTTP access to
that resource.
Privileges may be containers of other privileges, in which case
they are termed aggregate privileges. If a principal is
granted or denied an aggregate privilege, it is semantically
equivalent to granting or denying each of the aggregated
privileges individually. For example, an implementation may
define add-member and remove-member privileges that control the
ability to add and remove an internal member of a collection.
Since these privileges control the ability to update the state
of a collection, these privileges would be aggregated by the
DAV:write privilege on a collection, and granting the DAV:write
privilege on a collection would also grant the add-member and
remove-member privileges.
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Privileges may have the quality of being abstract, in which
case they cannot be set in an ACE. Aggregate and non-aggregate
privileges are both capable of being abstract. Abstract
privileges are useful for modeling privileges that otherwise
would not be exposed via the protocol. Abstract privileges also
provide server implementations with flexibility in implementing
the privileges defined in this specification. For example, if
a server is incapable of separating the read resource
capability from the read ACL capability, it can still model the
DAV:read and DAV:read-acl privileges defined in this
specification by declaring them abstract, and containing them
within a non-abstract aggregate privilege (say, read-all) that
holds DAV:read, and DAV:read-acl. In this way, it is possible
to set the aggregate privilege, read-all, thus coupling the
setting of DAV:read and DAV:read-acl, but it is not possible to
set DAV:read, or DAV:read-acl individually. Since aggregate
privileges can be abstract, it is also possible to use abstract
privileges to group or organize non-abstract privileges.
Privilege containment loops are not allowed, hence a privilege
MUST NOT contain itself. For example, DAV:read cannot contain
DAV:read.
The set of privileges that apply to a particular resource may
vary with the DAV:resourcetype of the resource, as well as
between different server implementations. To promote
interoperability, however, this specification defines a set of
well-known privileges (e.g. DAV:read,DAV:write, DAV:read-acl,
DAV:write-acl, DAV:read-current-user-privilege-set, and
DAV:all), which can at least be used to classify the other
privileges defined on a particular resource. The access
permissions on null and lock-null resources (defined in
[RFC2518], Sections 3 and 7.4) are solely those they inherit
(if any), and they are not discoverable (i.e., the access
control properties specified in Section 5 are not defined on
null and lock-null resources). On the transition from null or
lock-null to a stateful resource, the initial access control
list is set by the server's default ACL value policy (if any).
3.1 DAV:read Privilege
The read privilege controls methods that return information
about the state of the resource, including the resource's
properties. Affected methods include GET and PROPFIND.
Additionally, the read privilege MAY control the OPTIONS
method.
3.2 DAV:write Privilege
The write privilege controls methods that modify the content,
dead properties, or (in the case of a collection) membership of
the resource, such as PUT and PROPPATCH. Note that state
modification is also controlled via locking (see section 5.3 of
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[WEBDAV]), so effective write access requires that both write
privileges and write locking requirements are satisfied.
3.3 DAV:read-acl Privilege
The DAV:read-acl privilege controls the use of PROPFIND to
retrieve the DAV:acl property of the resource.
3.4 DAV:read-current-user-privilege-set Privilege
The DAV:read-current-user-privilege-set privilege controls the
use of PROPFIND to retrieve the DAV:current-user-privilege-set
property of the resource.
Clients are intended to use this property to visually indicate
in their UI items that are dependent on the permissions of a
resource, for example, by graying out resources that are not
writeable.
This privilege is separate from DAV:read-acl because there is a
need to allow most users access to the privileges permitted the
current user (due to its use in creating the UI), while the
full ACL contains information that may not be appropriate for
the current authenticated user. As a result, the set of users
who can view the full ACL is expected to be much smaller than
those who can read the current user privilege set, and hence
distinct privileges are needed for each.
3.5 DAV:write-acl Privilege
The DAV:write-acl privilege controls use of the ACL method to
modify the DAV:acl property of the resource.
3.6 DAV:all Privilege
DAV:all is an aggregate privilege that contains the entire set
of privileges that apply to the resource.
3.7 Aggregation of Predefined Privileges
Server implementations are free to aggregate the predefined
privileges (defined above in Sections 3.1-3.6) subject to the
following limitations:
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DAV:read-acl MUST NOT contain DAV:read, DAV:write, DAV:write-
acl, or DAV:read-current-user-privilege-set.
DAV:write-acl MUST NOT contain DAV:write, DAV:read, DAV:read-
acl, or DAV:read-current-user-privilege-set.
DAV:read-current-user-privilege-set MUST NOT contain DAV:write,
DAV:read, DAV:read-acl, or DAV:write-acl.
DAV:write MUST NOT contain DAV:read, DAV:read-acl, or DAV:read-
current-user-privilege-set.
DAV:read MUST NOT contain DAV:write, or DAV:write-acl.
4 PRINCIPAL PROPERTIES
Principals are manifested to clients as an HTTP resource,
identified by a URL. A principal MUST have a DAV:displayname
property (defined in Section 13.2 of [RFC2518]), and a
DAV:resourcetype property (defined in Section 13.9 of
[RFC2518]). Additionally, a principal MUST report the
DAV:principal empty XML element in the value of the
DAV:resourcetype property in addition to all other reported
elements. For example, a collection principal would report
DAV:collection and DAV:principal elements. The element type
declaration for DAV:principal is:
This protocol defines the following additional property for a
principal. Since it is expensive, for many servers, to retrieve
access control information, the name and value of this property
SHOULD NOT be returned by a PROPFIND allprop request (as
defined in Section 12.14.1 of [RFC2518]).
4.1 DAV:alternate-URL
This protected property, if non-empty, contains the URIs of
network resources with additional descriptive information about
the principal. This property identifies one or more additional
network resources (i.e., it contains one or more URIs) that may
be consulted by a client to gain additional knowledge
concerning a principal. Two potential uses for this property
are to store an ldap [RFC2255] or mailto [RFC2368] scheme URL.
Support for this property is REQUIRED, and the value is empty
if no alternate URL exists for the principal. .
5 ACCESS CONTROL PROPERTIES
This specification defines a number of new properties for
WebDAV resources. Access control properties may be retrieved
just like other WebDAV properties, using the PROPFIND method.
Since it is expensive, for many servers, to retrieve access
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control information, a PROPFIND allprop request (as defined in
Section 12.14.1 of [RFC2518]) SHOULD NOT return the names and
values of the properties defined in this section.
HTTP resources that support the WebDAV Access Control Protocol
MUST contain the following properties. Null, and lock-null
resources (described in Section 7.4 of [RFC2518]) MUST NOT
contain the following properties:
5.1 DAV:owner
This protected property identifies a particular principal as
being the "owner" of the resource. Since the owner of a
resource often has special access control capabilities (e.g.,
the owner frequently has permanent DAV:write-acl privilege),
clients might display the resource owner in their user
interface.
5.1.1 Example: Retrieving DAV:owner
This example shows a client request for the value of the
DAV:owner property from a collection resource with URL
http://www.webdav.org/papers/. The principal making the request
is authenticated using Digest authentication. The value of
DAV:owner is the URL http://www.webdav.org/_acl/users/gstein,
wrapped in the DAV:href XML element.
>> Request <<
PROPFIND /papers/ HTTP/1.1
Host: www.webdav.org
Content-type: text/xml; charset="utf-8"
Content-Length: xxx
Depth: 0
Authorization: Digest username="jim",
realm="jim@webdav.org", nonce="...",
uri="/papers/", response="...", opaque="..."
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
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http://www.webdav.org/papers/
HTTP/1.1 200 OK
http://www.webdav.org/_acl/users/gstein
5.1.2 Example: An Attempt to Set DAV:owner
The following example shows a client request to modify the
value of the DAV:owner property on the resource with URL
http://www.webdav.org/papers/. Since DAV:owner is a protected
property, the server responds with a 207 (Multi-Status)
response that contains a 403 (Forbidden) status code for the
act of setting DAV:owner. [RFC2518], Section 8.2.1 describes
PROPPATCH status code information, and Section 11 describes the
Multi-Status response.
>> Request <<
PROPPATCH /papers/ HTTP/1.1
Host: www.webdav.org
Content-type: text/xml; charset="utf-8"
Content-Length: xxx
Depth: 0
Authorization: Digest username="jim",
realm="jim@webdav.org", nonce="...",
uri="/papers/", response="...", opaque="..."
http://www.webdav.org/_acl/users/jim
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
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http://www.webdav.org/papers/
HTTP/1.1 403 Forbidden
Failure to set protected property
(DAV:owner)
5.2 DAV:supported-privilege-set
This is a protected property that identifies the privileges
defined for the resource.
Each privilege appears as an XML element, where aggregate
privileges list as sub-elements all of the privileges that they
aggregate.
An abstract privilege of a resource MUST NOT be used in an ACE
for that resource. Servers MUST fail an attempt to set an
abstract privilege.
A description is a human-readable description of what this
privilege controls access to.
It is envisioned that a WebDAV ACL-aware administrative client
would list the supported privileges in a dialog box, and allow
the user to choose non-abstract privileges to apply in an ACE.
The privileges tree is useful programmatically to map well-
known privileges (defined by WebDAV or other standards groups)
into privileges that are supported by any particular server
implementation. The privilege tree also serves to hide
complexity in implementations allowing large number of
privileges to be defined by displaying aggregates to the user.
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5.2.1 Example: Retrieving a List of Privileges Supported on a
Resource
This example shows a client request for the DAV:supported-
privilege-set property on the resource
http://www.webdav.org/papers/. The value of the DAV:supported-
privilege-set property is a tree of supported privileges:
DAV:all (aggregate, abstract)
|
+-- DAV:read (aggregate)
|
+-- DAV:read-acl (abstract)
+-- DAV:read-current-user-privilege-set (abstract)
+-- DAV:write (aggregate)
|
+-- DAV:write-acl (abstract)
This privilege tree is not normative, and many possible
privilege trees are possible.
>> Request <<
PROPFIND /papers/ HTTP/1.1
Host: www.webdav.org
Content-type: text/xml; charset="utf-8"
Content-Length: xxx
Depth: 0
Authorization: Digest username="gclemm",
realm="gclemm@webdav.org", nonce="...",
uri="/papers/", response="...", opaque="..."
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
http://www.webdav.org/papers/
HTTP/1.1 200 OK
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Any operation
Read any object
Read ACL
Read current user privilege set
property
Write any object
Write ACL
5.3 DAV:current-user-privilege-set
DAV:current-user-privilege-set is a protected property
containing the exact set of privileges (as computed by the
server) granted to the currently authenticated HTTP user.
Aggregate privileges and their contained privileges are listed.
A user-agent can use the value of this property to adjust its
user interface to make actions inaccessible (e.g., by graying
out a menu item or button) for which the current principal does
not have permission. This is particularly useful for an access
control user interface, which can be constructed without
knowing the ACE combining semantics of the server. This
property is also useful for determining what operations the
current principal can perform, without having to actually
execute an operation.
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If the current user is granted a specific privilege, that
privilege must belong to the set of privileges that may be set
on this resource. Therefore, each element in the DAV:current-
user-privilege-set property MUST identify a non-abstract
privilege from the DAV:supported-privilege-set property.
5.3.1 Example: Retrieving the User's Current Set of Assigned
Privileges
Continuing the example from Section 5.2.1, this example shows a
client requesting the DAV:current-user-privilege-set property
from the resource with URL http://www.webdav.org/papers/. The
username of the principal making the request is ôkhareö, and
Digest authentication is used in the request. The principal
with username ôkhareö has been granted the DAV:read privilege.
Since the DAV:read privilege contains the DAV:read-acl and
DAV:read-current-user-privilege-set privileges (see Section
5.2.1), the principal with username ôkhareö can read the ACL
property, and the DAV:current-user-privilege-set property.
However, the DAV:all, DAV:read-acl, DAV:write-acl and DAV:read-
current-user-privilege-set privileges are not listed in the
value of DAV:current-user-privilege-set, since (for this
example) they are abstract privileges. DAV:write is not listed
since the principal with username ôkhareö is not listed in an
ACE granting that principal write permission.
>> Request <<
PROPFIND /papers/ HTTP/1.1
Host: www.webdav.org
Content-type: text/xml; charset="utf-8"
Content-Length: xxx
Depth: 0
Authorization: Digest username="khare",
realm="khare@webdav.org", nonce="...",
uri="/papers/", response="...", opaque="..."
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
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http://www.webdav.org/papers/
HTTP/1.1 200 OK
5.4 DAV:acl
This is a protected property that specifies the list of access
control entries (ACEs), which define what principals are to get
what privileges for this resource.
Each DAV:ace element specifies the set of privileges to be
either granted or denied to a single principal. If the DAV:acl
property is empty, no principal is granted any privilege.
5.4.1 ACE Principal
The DAV:principal element identifies the principal to which
this ACE applies.
The current user matches DAV:href only if that user is
authenticated as being (or being a member of) the principal
identified by the URL contained by that DAV:href.
The current user always matches DAV:all.
The current user matches DAV:authenticated only if
authenticated.
The current user matches DAV:unauthenticated only if not
authenticated.
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DAV:all is the union of DAV:authenticated, and
DAV:unauthenticated. For a given request, the user matches
either DAV:authenticated, or DAV:unauthenticated, but not both
(that is, DAV:authenticated and DAV:unauthenticated are
disjoint sets).
The current user matches a DAV:property principal in a DAV:acl
property of a resource only if the value of the identified
property of that resource contains at most one DAV:href XML
element, the URI value of DAV:href identifies a principal, and
the current user is authenticated as being (or being a member
of) that principal. For example, if the DAV:property element
contained , the current user would match the
DAV:property principal only if the current user is
authenticated as matching the principal identified by the
DAV:owner property of the resource.
The current user matches DAV:self in a DAV:acl property of the
resource only if that resource is a principal object and the
current user is authenticated as being that principal or a
member of that principal collection.
5.4.2 ACE Grant and Deny
Each DAV:grant or DAV:deny element specifies the set of
privileges to be either granted or denied to the specified
principal. A DAV:grant or DAV:deny element of the DAV:acl of a
resource MUST only contain non-abstract elements specified in
the DAV:supported-privilege-set of that resource.
5.4.3 ACE Protection
If an ACE contains a DAV:protected element, an ACL request
without that ACE MUST fail.
5.4.4 ACE Inheritance
The presence of a DAV:inherited element indicates that this ACE
is inherited from another resource that is identified by the
URL contained in a DAV:href element. An inherited ACE cannot
be modified directly, but instead the ACL on the resource from
which it is inherited must be modified.
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Note that ACE inheritance is not the same as ACL
initialization. ACL initialization defines the ACL that a
newly created resource will use (if not specified). ACE
inheritance refers to an ACE that is logically shared - where
an update to the resource containing an ACE will affect the ACE
of each resource that inherits that ACE. The method by which
ACLs are initialized or by which ACEs are inherited is not
defined by this document.
5.4.5 Example: Retrieving a Resource's Access Control List
Continuing the example from Sections 5.2.1 and 5.3.1, this
example shows a client requesting the DAV:acl property from the
resource with URL http://www.webdav.org/papers/. There are two
ACEs defined in this ACL:
ACE #1: The principal collection identified by URL
http://www.webdav.org/_acl/groups/maintainers/ (the group of
site maintainers) is granted DAV:write privilege. Since (for
this example) DAV:write contains the DAV:write-acl privilege
(see Section 5.2.1), this means the ômaintainersö group can
also modify the access control list.
ACE #2: All principals (DAV:all) are granted the DAV:read
privilege. Since (for this example) DAV:read contains DAV:read-
acl and DAV:read-current-user-privilege-set, this means all
users (including all members of the ômaintainersö group) can
read the DAV:acl property and the DAV:current-user-privilege-
set property.
>> Request <<
PROPFIND /papers/ HTTP/1.1
Host: www.webdav.org
Content-type: text/xml; charset="utf-8"
Content-Length: xxx
Depth: 0
Authorization: Digest username="masinter",
realm="masinter@webdav.org", nonce="...",
uri="/papers/", response="...", opaque="..."
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
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Content-Length: xxx
http://www.webdav.org/papers/
HTTP/1.1 200 OK
http://www.webdav.org/_acl/groups/maintainers/
5.5 DAV:acl-semantics
This is a protected property that defines the ACL semantics.
These semantics define how multiple ACEs that match the current
user are combined, what are the constraints on how ACEs can be
ordered, and which principals must have an ACE. A client user
interface could use the value of this property to provide
feedback to a human operator concerning the impact of proposed
changes to an ACL. Alternately, a client can use this property
to help it determine, before submitting an ACL method
invocation, what ACL changes it needs to make to accomplish a
specific goal (or whether that goal is even achievable on this
server).
Since it is not practical to require all implementations to use
the same ACL semantics, the DAV:acl-semantics property is used
to identify the ACL semantics for a particular resource. The
DAV:acl-semantics element is defined in Section 6.
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5.5.1 Example: Retrieving DAV:acl-semantics
In this example, the client requests the value of the DAV:acl-
semantics property. Digest authentication provides credentials
for the principal operating the client. In this example, the
ACE combination semantics are DAV:first-match, described in
Section 6.1.1, the ACE ordering semantics are not specified
(some value other than DAV:deny-before-grant, described in
Section 6.2.1), the DAV:allowed-ace element states that only
one ACE is permitted for each principal, and an ACE describing
the privileges granted the DAV:all principal must exist in
every ACL.
>> Request <<
PROPFIND /papers/ HTTP/1.1
Host: www.webdav.org
Content-type: text/xml; charset="utf-8"
Content-Length: xxx
Depth: 0
Authorization: Digest username="srcarter",
realm="srcarter@webdav.org", nonce="...",
uri="/papers/", response="...", opaque="..."
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
http://www.webdav.org/papers/
HTTP/1.1 200 OK
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5.6 DAV:principal-collection-set
This protected property contains zero, one, or more URLs that
identify a collection principal. It is expected that
implementations of this protocol will typically use a
relatively small number of locations in the URL namespace for
principal, and collection principals. In cases where this
assumption holds, the DAV:principal-collection-set property
will contain a small set of URLs identifying the top of a
collection hierarchy containing multiple principals and
collection principals. An access control protocol user agent
could use the contents of DAV:principal-collection-set to query
the DAV:displayname property (specified in Section 13.2 of
[RFC2518]) of all principals on that server, thereby yielding
human-readable names for each principal that could be displayed
in a user interface.
Since different servers can control different parts of the URL
namespace, different resources on the same host MAY have
different DAV:principal-collection-set values. The collections
specified in the DAV:principal-collection-set MAY be located on
different hosts from the resource. The URLs in DAV:principal-
collection-set SHOULD be http or https scheme URLs. For
security and scalability reasons, a server MAY report only a
subset of the entire set of known collection principals, and
therefore clients should not assume they have retrieved an
exhaustive listing. Additionally, a server MAY elect to report
none of the collection principals it knows about, in which case
the property value would be empty.
5.6.1 Example: Retrieving DAV:principal-collection-set
In this example, the client requests the value of the
DAV:principal-collection-set property on the collection
resource identified by URL http://www.webdav.org/papers/. The
property contains the two URLs,
http://www.webdav.org/_acl/users/ and
http://www.webdav.org/_acl/groups/, both wrapped in
XML elements. Digest authentication provides credentials for
the principal operating the client.
The client might reasonably follow this request with two
separate PROPFIND requests to retrieve the DAV:displayname
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property of the members of the two collections (/_acl/users/
and /_acl_groups/). This information could be used when
displaying a user interface for creating access control
entries.
>> Request <<
PROPFIND /papers/ HTTP/1.1
Host: www.webdav.org
Content-type: text/xml; charset="utf-8"
Content-Length: xxx
Depth: 0
Authorization: Digest username="yarong",
realm="yarong@webdav.org", nonce="...",
uri="/papers/", response="...", opaque="..."
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
http://www.webdav.org/papers/
HTTP/1.1 200 OK
http://www.webdav.org/_acl/users/
http://www.webdav.org/_acl/groups/
5.7 Example: PROPFIND to retrieve access control properties
The following example shows how access control information can
be retrieved by using the PROPFIND method to fetch the values
of the DAV:owner, DAV:supported-privilege-set, DAV:current-
user-privilege-set, and DAV:acl properties.
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>> Request <<
PROPFIND /top/container/ HTTP/1.1
Host: www.foo.org
Content-type: text/xml; charset="utf-8"
Content-Length: xxx
Depth: 0
Authorization: Digest username="ejw",
realm="users@foo.org", nonce="...",
uri="/top/container/", response="...", opaque="..."
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
http://www.foo.org/top/container/
HTTP/1.1 200 OK
http://www.foo.org/users/gclemm
Any operation
Read any object
Write any object
Create an object
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Update an object
Delete an object
Read the ACL
Write the ACL
http://www.foo.org/users/esedlar
http://www.foo.org/groups/marketing/
http://www.foo.org/top/
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The value of the DAV:owner property is a single DAV:href XML
element containing the URL of the principal that owns this
resource.
The value of the DAV:supported-privilege-set property is a tree
of supported privileges:
DAV:all (aggregate, abstract)
|
+-- DAV:read
+-- DAV:write (aggregate, abstract)
|
+-- http://www.webdav.org/acl/create
+-- http://www.webdav.org/acl/update
+-- http://www.webdav.org/acl/delete
+-- DAV:read-acl
+-- DAV:write-acl
The DAV:current-user-privilege-set property contains two
privileges, DAV:read, and DAV:read-acl. This indicates that the
current authenticated user only has the ability to read the
resource, and read the DAV:acl property on the resource.
The DAV:acl property contains a set of four ACEs:
ACE #1: The principal identified by the URL
http://www.foo.org/users/esedlar is granted the DAV:read,
DAV:write, and DAV:read-acl privileges.
ACE #2: The principals identified by the URL
http://www.foo.org/groups/marketing/ are denied the DAV:read
privilege. In this example, the principal URL identifies a
group, which is represented by a collection principal.
ACE #3: In this ACE, the principal is a property principal,
specifically the DAV:owner property. When evaluating this ACE,
the value of the DAV:owner property is retrieved, and is
examined to see if it contains a DAV:href XML element. If so,
the URL within the DAV:href element is read, and identifies a
principal. In this ACE, the owner is granted DAV:read-acl, and
DAV:write-acl privileges.
ACE #4: This ACE grants the DAV:all principal (all users) the
DAV:read privilege. This ACE is inherited from the resource
http://www.foo.org/top/, the parent collection of this
resource.
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6 ACL SEMANTICS
The ACL semantics define how multiple ACEs that match the
current user are combined, what are the constraints on how ACEs
can be ordered, and which principals must have an ACE.
6.1 ACE Combination
The DAV:ace-combination element defines how privileges from
multiple ACEs that match the current user will be combined to
determine the access privileges for that user. Multiple ACEs
may match the same user because the same principal can appear
in multiple ACEs, because multiple principals can identify the
same user, and because one principal can be a member of another
principal.
6.1.1 DAV:first-match ACE Combination
The ACEs are evaluated in the order in which they appear in the
ACL. If the first ACE that matches the current user does not
grant all the privileges needed for the request, the request
MUST fail.
6.1.2 DAV:all-grant-before-any-deny ACE Combination
The ACEs are evaluated in the order in which they appear in the
ACL. If an evaluated ACE denies a privilege needed for the
request, the request MUST fail. If all ACEs have been
evaluated without the user being granted all privileges needed
for the request, the request MUST fail.
6.1.3 DAV:specific-deny-overrides-grant ACE Combination
All ACEs in the ACL are evaluated. An "individual ACE" is one
whose principal identifies the current user. A "group ACE" is
one whose principal is a collection that contains a principal
that identifies the current user. A privilege is granted if it
is granted by an individual ACE and not denied by an individual
ACE, or if it is granted by a group ACE and not denied by an
individual or group ACE. A request MUST fail if any of its
needed privileges are not granted.
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6.2 ACE Ordering
The DAV:ace-ordering element defines a constraint on how the
ACEs can be ordered in the ACL.
6.2.1 DAV:deny-before-grant ACE Ordering
This element indicates that all deny ACEs must precede all
grant ACEs.
6.3 Allowed ACE
The DAV:allowed-ace XML element specifies constraints on what
kinds of ACEs are allowed in an ACL.
6.3.1 DAV:principal-only-one-ace ACE Constraint
This element indicates that a principal can appear in only one
ACE per resource.
6.3.2 DAV:grant-only ACE Constraint
This element indicates that ACEs with deny clauses are not
allowed.
6.4 Required Principals
The required principal elements identify which principals must
have an ACE defined in the ACL.
For example, the following element requires that the ACL
contain a DAV:owner property ACE:
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7 ACCESS CONTROL AND EXISTING METHODS
This section defines the impact of access control functionality
on existing methods.
7.1 OPTIONS
If the server supports access control, it MUST return "access-
control" as a field in the DAV response header from an OPTIONS
request on any resource implemented by that server.
7.1.1 Example - OPTIONS
>> Request <<
OPTIONS /foo.html HTTP/1.1
Host: www.webdav.org
Content-Length: 0
>> Response <<
HTTP/1.1 200 OK
DAV: 1, 2, access-control
Allow: OPTIONS, GET, PUT, PROPFIND, PROPPATCH, ACL
In this example, the OPTIONS response indicates that the server
supports access control and that /foo.html can have its access
control list modified by the ACL method.
7.2 MOVE
When a resource is moved from one location to another due to a
MOVE request, the non-inherited ACEs in the DAV:acl property of
the resource MUST NOT be modified, or the MOVE request fails.
7.3 COPY
The DAV:acl property on the resource at the destination of a
COPY MUST be the same as if the resource was created by an
individual resource creation request (e.g. MKCOL, PUT).
8 ACCESS CONTROL METHODS
8.1 ACL
The ACL method modifies the access control list (which can be
read via the DAV:acl property) of a resource. Specifically,
the ACL method only permits modification to ACEs that are not
inherited, and are not protected. An ACL method invocation
modifies all non-inherited and non-protected ACEs in a
resource's access control list to exactly match the ACEs
contained within in the DAV:acl XML element (specified in
Section 5.4) of the request body. An ACL request body MUST
contain only one DAV:acl XML element. Unless the non-inherited
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and non-protected ACEs of the DAV:acl property of the resource
can be updated to be exactly the value specified in the ACL
request, the ACL request MUST fail.
It is possible that the ACEs visible to the current user in the
DAV:acl property may only be a portion of the complete set of
ACEs on that resource. If this is the case, an ACL request only
modifies the set of ACEs visible to the current user, and does
not affect any non-visible ACE.
In order to avoid overwriting DAV:acl changes by another
client, a client SHOULD acquire a WebDAV lock on the resource
before retrieving the DAV:acl property of a resource that it
intends on updating.
Implementation Note: Two common operations are to add or
remove an ACE from an existing access control list. To
accomplish this, a client uses the PROPFIND method to
retrieve the value of the DAV:acl property, then parses the
returned access control list to remove all inherited and
protected ACEs (these ACEs are tagged with the DAV:inherited
and DAV:protected XML elements). In the remaining set of non-
inherited, non-protected ACEs, the client can add or remove
one or more ACEs before submitting the final ACE set in the
request body of the ACL method.
8.1.1 ACL Preconditions
An implementation MAY enforce one or more of the following
constraints on an ACL request. If the constraint is violated,
a 403 (Forbidden) response MUST be returned and the indicated
XML element MUST be returned as the top level element in an XML
response body.
: A conflict exists between two or more ACEs
submitted in the ACL request.
: A conflict exists between an ACE
in the ACL request and a protected ACE on the resource. For
example, if the resource has a protected ACE granting DAV:write
to a given principal, then it would be a protected ACE conflict
if the ACL request submitted an ACE denying DAV:write to the
same principal.
: A conflict exists between an ACE
in the ACL request and an inherited ACE on the resource. For
example, if the resource inherits an ACE from its parent
collection granting DAV:write to a given principal, then it
would be an inherited ACE conflict if the ACL request submitted
an ACE denying DAV:write to the same principal. Note that
reporting of this error will be implementation-dependent.
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Implementations have the choice to either report this error, or
to allow the ACE to be set, and then let normal ACE evaluation
rules determine whether the new ACE has any impact on the
privileges available to a specific principal.
: An implementation MAY limit the number of
ACEs in an ACL. However, ACL-compliant servers MUST support at
least one ACE granting privileges to a single principal, and
one ACE granting privileges to a collection principal.
: All non-inherited deny ACEs MUST
precede all non-inherited grant ACEs.
: For implementations that have
the DAV:principal-only-one-ace constraint (defined in Section
6.3.1), this XML element indicates that fulfilling the ACL
request would result in multiple ACEs for one or more
principals.
: For implementations that have the DAV:grant-
only constraint (defined in Section 6.3.2), this XML element
indicates the request contained one or more deny ACEs.
: One or more required principals (see
Section 6.4) would not be present in the access control list
after processing the ACL request. The DAV:required-principal
XML element MUST contain a list of the missing principal(s),
following the syntax specified in Section 6.4.
8.1.2 Example: the ACL method
In the following example, user "fielding", authenticated by
information in the Authorization header, grants the principal
identified by the URL http://www.foo.org/users/esedlar (i.e.,
the user "esedlar") read and write privileges, grants the owner
of the resource read-acl and write-acl privileges, and grants
everyone read privileges.
>> Request <<
ACL /top/container/ HTTP/1.1
Host: www.foo.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Authorization: Digest username="fielding",
realm="users@foo.org", nonce="...",
uri="/top/container/", response="...", opaque="..."
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http://www.foo.org/users/esedlar
>> Response <<
HTTP/1.1 200 OK
8.1.3 Example: ACL method failure due to protected ACE conflict
In the following request, user "fielding", authenticated by
information in the Authorization header, attempts to deny the
principal identified by the URL
http://www.foo.org/users/esedlar (i.e., the user "esedlar")
write privileges. Prior to the request, the DAV:acl property on
the resource contained a protected ACE (see Section 5.4.3)
granting DAV:owner the DAV:read and DAV:write privileges. The
principal identified by URL http://www.foo.org/users/esedlar is
the owner of the resource. The ACL method invocation fails
because the submitted ACE conflicts with the protected ACE,
thus violating the semantics of ACE protection.
>> Request <<
ACL /top/container/ HTTP/1.1
Host: www.foo.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Authorization: Digest username="fielding",
realm="users@foo.org", nonce="...",
uri="/top/container/", response="...", opaque="..."
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http://www.foo.org/users/esedlar
>> Response <<
HTTP/1.1 403 Forbidden
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
8.1.4 Example: ACL method failure due to an inherited ACE conflict
In the following request, user "ejw", authenticated by
information in the Authorization header, tries to change the
access control list on the resource
http://www.foo.org/top/index.html. This resource has two
inherited ACEs.
Inherited ACE #1 grants the principal identified by URL
http://www.foo.org/users/ejw (i.e., the user "ejw")
http://www.foo.org/privs/write-all and DAV:read-acl privileges.
On this server, http://www.foo.org/privs/write-all is an
aggregate privilege containing DAV:write, and DAV:write-acl.
Inherited ACE #2 grants principal DAV:all the DAV:read
privilege.
The request attempts to set a (non-inherited) ACE, denying the
principal identified by the URL http://www.foo.org/users/ejw
(i.e., the user ôejwö) DAV:write permission. This conflicts
with inherited ACE #1. Note that the decision to report an
inherited ACE conflict is specific to this server
implementation. Another server implementation could have
allowed the new ACE to be set, and then used normal ACE
evaluation rules to determine whether the new ACE has any
impact on the privileges available to a principal.
>> Request <<
ACL /top/index.html HTTP/1.1
Host: www.foo.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Authorization: Digest username="ejw",
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realm="users@foo.org", nonce="...",
uri="/top/index.html", response="...", opaque="..."
http://www.foo.org/users/ejw
>> Response <<
HTTP/1.1 403 Forbidden
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
8.1.5 Example: ACL method failure due to an attempt to set grant and
deny in a single ACE.
In this example, user "ygoland", authenticated by information
in the Authorization header, tries to change the access control
list on the resource http://www.foo.org/diamond/engagement-
ring.gif. The ACL request includes a single, syntactically and
semantically incorrect ACE, which attempts to grant the
collection principal identified by the URL
http://www.foo.org/users/friends/ DAV:read privilege and deny
the principal identified by URL
http://www.foo.org/users/ygoland-so (i.e., the user "ygoland-
so") DAV:read privilege. However, it is illegal to have
multiple principal elements, as well as both a grant and deny
element in the same ACE, so the request fails due to poor
syntax.
>> Request <<
ACL /diamond/engagement-ring.gif HTTP/1.1
Host: www.foo.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
Authorization: Digest username="ygoland",
realm="users@foo.org", nonce="...",
uri="/diamond/engagement-ring.gif", response="...",
opaque="..."
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http://www.foo.org/users/friends/
http://www.foo.org/users/ygoland-so
>> Response <<
HTTP/1.1 400 Bad Request
Content-Length: 0
Note that if the request had been divided into two ACEs, one to
grant, and one to deny, the request would have been
syntactically well formed.
9 ACCESS CONTROL REPORTS
9.1 REPORT Method
A REPORT request is an extensible mechanism for obtaining
information about a resource. Unlike a resource property,
which has a single value, the value of a report can depend on
additional information specified in the REPORT request body and
in the REPORT request headers.
Marshalling:
The body of a REPORT request specifies which report is being
requested, as well as any additional information that will be
used to customize the report.
The request MAY include a Depth header.
The response body for a successful request MUST contain the
requested report.
If a Depth request header is included, the response MUST be a
207 Multi-Status.
Postconditions:
The REPORT method MUST NOT change the content or dead
properties of any resource.
If a Depth request header is included, the request MUST be
applied separately to the collection itself and to all members
of the collection that satisfy the Depth value. The DAV:prop
element of a DAV:response for a given resource MUST contain the
requested report for that resource.
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9.2 DAV:acl-principal-props Report
The DAV:acl-principle-props report returns, for all principals
in the DAV:acl property that are identified by http(s) URLs,
the value of the properties specified in the REPORT request
body. In the case where a principal URL appears multiple times,
the DAV:acl-principal-props report MUST return the properties
for that principal only once.
Marshalling
The request body MUST be a DAV:acl-principal-props XML element.
ANY value: a sequence of one or more elements, with at most one
DAV:prop element.
prop: see RFC 2518, Section 12.11
The response body for a successful request MUST be a
DAV:multistatus XML element (i.e., the response uses the same
format as the response for PROPFIND).
multistatus: see RFC 2518, Section 12.9
The response body for a successful DAV:acl-principal-props
REPORT request MUST contain a DAV:response element for each
principal identified by an http(s) URL listed in a
DAV:principal XML element of an ACE within the DAV:acl property
of the resource identified by the Request-URI.
9.2.1 Example: DAV:acl-principal-props Report
Resource http;//www.webdav.org/index.html has an ACL with three
ACEs:
ACE #1: All principals (DAV:all) have DAV:read and DAV:read-
current-user-privilege-set access.
ACE #2: The principal identified by
http://www.webdav.org/people/gstein (the user ôgsteinö) is
granted DAV:write, DAV:write-acl, DAV:read-acl privileges.
ACE #3: The collection principal identified by
http://www.webdav.org/groups/authors/ (the ôauthorsö group) is
granted DAV:write and DAV:read-acl privileges.
The following example shows a DAV:acl-principal-props report
requesting the DAV:displayname property. It returns the value
of DAV:displayname for resources
http://www.webdav.org/people/gstein and
http://www.webdav.org/groups/authors/ , but not for DAV:all,
since this is not an http(s) URL.
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>> Request <<
REPORT /index.html HTTP/1.1
Host: www.webdav.org
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://www.webdav.org/people/gstein
Greg Stein
HTTP/1.1 200 OK
http://www.webdav.org/groups/authors/
Site authors
HTTP/1.1 200 OK
9.3 DAV:principal-match REPORT
The DAV:principal-match REPORT is used to identify all members
of a collection that match the current user. In particular, if
the collection contains principals, the report can be used to
identify all members of the collection that match the current
user. Alternatively, if the collection contains resources that
have a property that identifies a principal (e.g. DAV:owner),
then the report can be used to identify all members of the
collection whose property identifies a principal that matches
the current user. For example, this report can return all of
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the resources in a collection hierarchy that are owned by the
current user.
Marshalling:
The request body MUST be a DAV:principal-match XML element.
ANY value: an element whose value identifies a property. The
expectation is the value of the named property typically
contains an href element that contains the URI of a principal
prop: see RFC 2518, Section 12.11
The response body for a successful request MUST be a
DAV:multistatus XML element.
multistatus: see RFC 2518, Section 12.9
The response body for a successful DAV:principal-match REPORT
request MUST contain a DAV:response element for each member of
the collection that matches the current user. When the
DAV:principal-property element is used, a match occurs if the
current user is the same as the principal identified by the URI
found in the DAV:href element of the property identified by the
DAV:principal-property element. When the DAV:self element is
used in a DAV:principal-match report issued against a
collection principal, it matches a child of the collection
principal if that child (a principal resource) identifies the
same principal as the current user.
If DAV:prop is specified in the request body, the properties
specified in the DAV:prop element MUST be reported in the
DAV:response elements.
9.3.1 Example: DAV:principal-match REPORT
The following example identifies the members of the collection
identified by the URL http://www.webdav.org/doc/ that are owned
by the current user. The current user (ôgclemmö) is
authenticated using Digest authentication.
>> Request <<
REPORT /doc/ HTTP/1.1
Host: www.webdav.org
Authorization: Digest username="gclemm",
realm="gclemm@webdav.org", nonce="...",
uri="/papers/", response="...", opaque="..."
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
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>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxxx
http://www.webdav.org/doc/foo.html
HTTP/1.1 200 OK
http://www.webdav.org/doc/img/bar.gif
HTTP/1.1 200 OK
10 XML PROCESSING
Implementations of this specification MUST support the XML
element ignore rule, as specified in Section 23.3.2 of
[RFC2518], and the WebDAV XML Namespace interpretation
convention, described in Section 23.4 of [RFC2518].
11 INTERNATIONALIZATION CONSIDERATIONS
In this specification, the only human-readable content can be
found in the description XML element, found within the
DAV:supported-privilege-set property. This element contains a
human-readable description of the capabilities controlled by a
privilege. As a result, the description element must be
capable of representing descriptions in multiple character
sets. Since the description element is found within a WebDAV
property, it is represented on-the-wire as XML [REC-XML], and
hence can leverage XML's language tagging and character set
encoding capabilities. Specifically, XML processors must, at
minimum, be able to read XML elements encoded using the UTF-8
[UTF-8] encoding of the ISO 10646 multilingual plane. XML
examples in this specification demonstrate use of the charset
parameter of the Content-Type header, as defined in [RFC3023],
as well as the XML "encoding" attribute, which together provide
charset identification information for MIME and XML processors.
For XML elements other than the description element, it is
expected that implementations will treat the property names,
privilege names, and values as tokens, and convert these tokens
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into human-readable text in the user's language and character
set when displayed to a person. Only a generic WebDAV property
display utility would display these values in their raw form to
a human user.
For error reporting, we follow the convention of HTTP/1.1
status codes, including with each status code a short, English
description of the code (e.g., 200 (OK)). While the
possibility exists that a poorly crafted user agent would
display this message to a user, internationalized applications
will ignore this message, and display an appropriate message in
the user's language and character set.
Further internationalization considerations for this protocol
are described in the WebDAV Distributed Authoring protocol
specification [RFC2518].
12 SECURITY CONSIDERATIONS
Applications and users of this access control protocol should
be aware of several security considerations, detailed below. In
addition to the discussion in this document, the security
considerations detailed in the HTTP/1.1 specification
[RFC2616], the WebDAV Distributed Authoring Protocol
specification [RFC2518], and the XML Media Types specification
[RFC3023] should be considered in a security analysis of this
protocol.
12.1 Increased Risk of Compromised Users
In the absence of a mechanism for remotely manipulating access
control lists, if a single user's authentication credentials
are compromised, only those resources for which the user has
access permission can be read, modified, moved, or deleted.
With the introduction of this access control protocol, if a
single compromised user has the ability to change ACLs for a
broad range of other users (e.g., a super-user), the number of
resources that could be altered by a single compromised user
increases. This risk can be mitigated by limiting the number of
people who have write-acl privileges across a broad range of
resources.
12.2 Risks of the DAV:read-acl and DAV:current-user-privilege-set
Privileges
The ability to read the access privileges (stored in the
DAV:acl property), or the privileges permitted the currently
authenticated user (stored in the DAV:current-user-privilege-
set property) on a resource may seem innocuous, since reading
an ACL cannot possibly affect the resource's state. However, if
all resources have world-readable ACLs, it is possible to
perform an exhaustive search for those resources that have
inadvertently left themselves in a vulnerable state, such as
being world-writeable. In particular, the property retrieval
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method PROPFIND, executed with Depth infinity on an entire
hierarchy, is a very efficient way to retrieve the DAV:acl or
DAV:current-user-privilege-set properties. Once found, this
vulnerability can be exploited by a denial of service attack in
which the open resource is repeatedly overwritten. Alternately,
writeable resources can be modified in undesirable ways.
To reduce this risk, read-acl privileges should not be granted
to unauthenticated principals, and restrictions on read-acl and
cuprivset privileges for authenticated principals should be
carefully analyzed when deploying this protocol. Access to the
current-user-privilege-set property will involve a tradeoff of
usability versus security. When the current-user-privilege-set
is visible, user interfaces are expected to provide enhanced
information concerning permitted and restricted operations, yet
this information may also indicate a vulnerability that could
be exploited. Deployment of this protocol will need to evaluate
this tradeoff in light of the requirements of the deployment
environment.
12.3 No Foreknowledge of Initial ACL
In an effort to reduce protocol complexity, this protocol
specification intentionally does not address the issue of how
to manage or discover the initial ACL that is placed upon a
resource when it is created. The only way to discover the
initial ACL is to create a new resource, then retrieve the
value of the DAV:acl property. This assumes the principal
creating the resource also has been granted the DAV:read-acl
privilege.
As a result, it is possible that a principal could create a
resource, and then discover that its ACL grants privileges that
are undesirable. Furthermore, this protocol makes it possible
(though unlikely) that the creating principal could be unable
to modify the ACL, or even delete the resource. Even when the
ACL can be modified, there will be a short period of time when
the resource exists with the initial ACL before its new ACL can
be set.
Several factors mitigate this risk. Human principals are often
aware of the default access permissions in their editing
environments and take this into account when writing
information. Furthermore, default privilege policies are
usually very conservative, limiting the privileges granted by
the initial ACL.
13 AUTHENTICATION
Authentication mechanisms defined in WebDAV also apply to this
WebDAV Access Control Protocol, in particular the Basic and
Digest authentication mechanisms defined in [RFC2617].
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14 IANA CONSIDERATIONS
This document uses the namespace defined by [RFC2518] for XML
elements. All other IANA considerations mentioned in [RFC2518]
also applicable to WebDAV ACL.
15 INTELLECTUAL PROPERTY
The following notice is copied from RFC 2026, section 10.4, and
describes the position of the IETF concerning intellectual
property claims made against this document.
The IETF takes no position regarding the validity or scope of
any intellectual property or other rights that might be claimed
to pertain to the implementation or use other technology
described in this document or the extent to which any license
under such rights might or might not be available; neither does
it represent that it has made any effort to identify any such
rights. Information on the IETF's procedures with respect to
rights in standards-track and standards-related documentation
can be found in BCP-11. Copies of claims of rights made
available for publication and any assurances of licenses to be
made available, or the result of an attempt made to obtain a
general license or permission for the use of such proprietary
rights by implementers or users of this specification can be
obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention
any copyrights, patents or patent applications, or other
proprietary rights that may cover technology that may be
required to practice this standard. Please address the
information to the IETF Executive Director.
16 ACKNOWLEDGEMENTS
This protocol is the collaborative product of the WebDAV ACL
design team: Bernard Chester, Geoff Clemm, Anne Hopkins, Barry
Lind, Sean Lyndersay, Eric Sedlar, Greg Stein, and Jim
Whitehead. The authors are grateful for the detailed review and
comments provided by Jim Amsden, Gino Basso, Murthy
Chintalapati, Dennis Hamilton, Laurie Harper, Ron Jacobs, Chris
Knight, Remy Maucherat, Larry Masinter, Yaron Goland, Lisa
Dusseault, and Joe Orton. Prior work on WebDAV access control
protocols has been performed by Yaron Goland, Paul Leach, Lisa
Dusseault, Howard Palmer, and Jon Radoff. We would like to
acknowledge the foundation laid for us by the authors of the
WebDAV and HTTP protocols upon which this protocol is layered,
and the invaluable feedback from the WebDAV working group.
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17 REFERENCES
17.1 Normative References
[RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
Requirement Levels." RFC 2119, BCP 14, Harvard, March, 1997.
[REC-XML] T. Bray, J. Paoli, C.M. Sperberg-McQueen, "Extensible
Markup Language (XML)." World Wide Web Consortium
Recommendation REC-xml-19980210. http://www.w3.org/TR/REC-xml-
19980210.
[RFC2616] R. Fielding, J. Gettys, J. C. Mogul, H. Frystyk, L.
Masinter, P. Leach, and T. Berners-Lee, "Hypertext Transfer
Protocol -- HTTP/1.1." RFC 2616. U.C. Irvine, Compaq, Xerox,
Microsoft, MIT/LCS, June, 1999.
[RFC2617] J. Franks, P. Hallam-Baker, J. Hostetler, S.
Lawrence, P. Leach, A. Luotonen, L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication." RFC
2617. Northwestern University, Verisign, AbiSource, Agranat,
Microsoft, Netscape, Open Market, June, 1999.
[RFC2518] Y. Goland, E. Whitehead, A. Faizi, S. R. Carter, D.
Jensen, "HTTP Extensions for Distributed Authoring -- WEBDAV."
RFC 2518. Microsoft, U.C. Irvine, Netscape, Novell, February,
1999.
[RFC2368] P. Hoffman, L. Masinter, J. Zawinski, "The mailto URL
scheme." RFC 2368. Internet Mail Consortium, Xerox, Netscape,
July, 1998.
[RFC2255] T. Howes, M. Smith, "The LDAP URL Format." RFC 2255.
Netscape, December, 1997.
[RFC3023] M. Murata, S. St.Laurent, D. Kohn, "XML Media Types."
RFC 3023. IBM Tokyo Research Laboratory, simonstl.com, Skymoon
Ventures, January, 2001.
[UTF-8] F. Yergeau, "UTF-8, a transformation format of Unicode
and ISO 10646." RFC 2279. Alis Technologies. January, 1998.
17.2 Informational References
[RFC2026] S.Bradner, "The Internet Standards Process û Revision
3." RFC 2026, BCP 9. Harvard, October, 1996.
18 AUTHORS' ADDRESSES
Geoffrey Clemm
Rational Software
20 Maguire Road
Lexington, MA 02421
Email: geoffrey.clemm@rational.com
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Anne Hopkins
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Email: annehop@microsoft.com
Eric Sedlar
Oracle Corporation
500 Oracle Parkway
Redwood Shores, CA 94065
Email: esedlar@us.oracle.com
Jim Whitehead
U.C. Santa Cruz
Dept. of Computer Science
Baskin Engineering
1156 High Street
Santa Cruz, CA 95064
Email: ejw@cse.ucsc.edu
19 APPENDICIES
19.1 XML Document Type Definition
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ANY value: a sequence of one or more elements, with at most one
DAV:prop element.
ANY value: an element whose value identifies a property. The
expectation is the value of the named property typically
contains an href element that contains the URI of a principal
20 NOTE TO RFC EDITOR
*** This section (Section 20) MUST be removed before
publication as an RFC ***
Section 9.1 defines the REPORT method. The REPORT method is
also defined in draft-ietf-deltav-versioning-15, in Section
3.6, using identical text. This was done to avoid making this
specification dependent on draft-ietf-deltav-versioning.
If draft-ietf-deltav-versioning is published as an RFC before
this specification, Section 9.1 MUST be removed.
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