--- 1/draft-ietf-webdav-acl-04.txt 2006-02-05 02:10:08.000000000 +0100
+++ 2/draft-ietf-webdav-acl-05.txt 2006-02-05 02:10:08.000000000 +0100
@@ -1,28 +1,28 @@
INTERNET-DRAFT Geoffrey Clemm, Rational Software
- draft-ietf-webdav-acl-04 Anne Hopkins, Microsoft Corporation
+draft-ietf-webdav-acl-05 Anne Hopkins, Microsoft Corporation
Eric Sedlar, Oracle Corporation
Jim Whitehead, U.C. Santa Cruz
- Expires July 21, 2001 January 21, 2001
+Expires July 21, 2001 April 23, 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-Drafts.
+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
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate 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
@@ -33,485 +33,566 @@
This document specifies a set of methods, headers, and message bodies
that define the WebDAV Access Control extensions to the HTTP/1.1
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/.
+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/.
Clemm, Hopkins, Sedlar, Whitehead [Page 1]
+
Table of Contents
- 1 INTRODUCTION......................................................3
- 1.1 Terms..........................................................4
- 1.2 Notational Conventions.........................................5
+1 INTRODUCTION......................................................4
+1.1 Terms...........................................................5
+1.2 Notational Conventions..........................................6
- 2 PRINCIPALS........................................................5
+2 PRINCIPALS........................................................6
- 3 PRIVILEGES........................................................5
- 3.1 DAV:read Privilege.............................................6
- 3.2 DAV:write Privilege............................................6
- 3.3 DAV:read-acl Privilege.........................................7
- 3.4 DAV:write-acl Privilege........................................7
- 3.5 DAV:all Privilege..............................................7
+3 PRIVILEGES........................................................6
+3.1 DAV:read Privilege..............................................7
+3.2 DAV:write Privilege.............................................7
+3.3 DAV:read-acl Privilege..........................................8
+3.4 DAV:read-cuprivset Privilege....................................8
+3.5 DAV:write-acl Privilege.........................................8
+3.6 DAV:all Privilege...............................................8
- 4 PRINCIPAL PROPERTIES..............................................7
- 4.1 DAV:is-principal...............................................7
- 4.2 DAV:authentication-id..........................................7
+4 PRINCIPAL PROPERTIES..............................................8
+4.1 DAV:is-principal................................................9
+4.2 DAV:alternate-URL...............................................9
- 5 ACCESS CONTROL PROPERTIES.........................................8
- 5.1 DAV:owner......................................................8
- 5.2 DAV:supported-privilege-set....................................8
- 5.3 DAV:current-user-privilege-set.................................9
- 5.4 DAV:acl........................................................9
- 5.4.1 ACE Principal................................................9
- 5.4.2 ACE Grant and Deny..........................................10
- 5.4.3 ACE Protection..............................................11
- 5.4.4 ACE Inheritance.............................................11
- 5.5 DAV:acl-semantics.............................................11
- 5.6 DAV:principal-collection-set..................................11
- 5.7 Example: PROPFIND to retrieve access control properties.......12
+5 ACCESS CONTROL PROPERTIES.........................................9
+5.1 DAV:owner.......................................................9
+5.2 DAV:supported-privilege-set....................................10
+5.3 DAV:current-user-privilege-set.................................11
+5.4 DAV:acl........................................................11
+ 5.4.1 ACE Principal...............................................11
+ 5.4.2 ACE Grant and Deny..........................................13
+ 5.4.3 ACE Protection..............................................13
+ 5.4.4 ACE Inheritance.............................................13
+5.5 DAV:acl-semantics..............................................13
+5.6 DAV:principal-collection-set...................................14
+5.7 Example: PROPFIND to retrieve access control properties........14
- 6 ACL SEMANTICS....................................................15
- 6.1 ACE Combination...............................................15
- 6.1.1 DAV:first-match ACE Combination.............................15
- 6.1.2 DAV:all-grant-before-any-deny ACE Combination...............15
- 6.1.3 DAV:no-deny ACE Combination.................................15
- 6.2 ACE Ordering..................................................16
- 6.2.1 DAV:deny-before-grant ACE Ordering..........................16
- 6.3 Required Principals...........................................16
+6 ACL SEMANTICS....................................................17
+6.1 ACE Combination................................................17
+ 6.1.1 DAV:first-match ACE Combination.............................18
+ 6.1.2 DAV:all-grant-before-any-deny ACE Combination...............18
+ 6.1.3 DAV:specific-deny-overrides-grant ACE Combination...........18
+6.2 ACE Ordering...................................................18
+ 6.2.1 DAV:deny-before-grant ACE Ordering..........................18
+6.3 Required Principals............................................18
- 7 ACCESS CONTROL AND EXISTING METHODS..............................16
- 7.1 OPTIONS.......................................................16
- 7.1.1 Example - OPTIONS...........................................16
+7 ACCESS CONTROL AND EXISTING METHODS..............................19
+7.1 OPTIONS........................................................19
+ 7.1.1 Example - OPTIONS...........................................19
- 8 ACCESS CONTROL METHODS...........................................17
- 8.1 ACL...........................................................17
- 8.1.1 ACL Preconditions...........................................17
- 8.1.2 Example: the ACL method.....................................17
- 8.1.3 Example: ACL method failure due to omission of protected ACE18
+8 ACCESS CONTROL METHODS...........................................19
+8.1 ACL............................................................19
+ 8.1.1 ACL Preconditions...........................................20
+ 8.1.2 Example: the ACL method.....................................20
+ 8.1.3 Example: ACL method failure due to omission of protected ACE21
8.1.4 Example: ACL method failure due to inherited ACEs preceding
- non-inherited ACEs................................................19
- 8.1.5 Example: ACL method failure due to an attempt to set grant and
- deny in a single ACE..............................................20
+ non-inherited ACEs................................................22
Clemm, Hopkins, Sedlar, Whitehead [Page 2]
- 9 INTERNATIONALIZATION CONSIDERATIONS..............................21
+ 8.1.5 Example: ACL method failure due to an attempt to set grant and
+ deny in a single ACE..............................................23
- 10 SECURITY CONSIDERATIONS........................................22
- 10.1 Increased Risk of Compromised Users...........................22
- 10.2 Authentication-id Property and Dictionary Attacks.............22
- 10.3 Risks of the read-acl Privilege...............................23
+9 INTERNATIONALIZATION CONSIDERATIONS..............................24
- 11 AUTHENTICATION.................................................23
+10 SECURITY CONSIDERATIONS........................................25
+10.1 Increased Risk of Compromised Users...........................25
+10.2 Risks of the read-acl and cuprivset Privileges................25
- 12 IANA CONSIDERATIONS............................................23
+11 AUTHENTICATION.................................................26
- 13 INTELLECTUAL PROPERTY..........................................23
+12 IANA CONSIDERATIONS............................................26
- 14 ACKNOWLEDGEMENTS...............................................24
+13 INTELLECTUAL PROPERTY..........................................26
- 15 REFERENCES.....................................................24
- 15.1 Normative References..........................................24
- 15.2 Informational References......................................25
+14 ACKNOWLEDGEMENTS...............................................26
- 16 AUTHORS' ADDRESSES.............................................25
+15 REFERENCES.....................................................27
+15.1 Normative References..........................................27
+15.2 Informational References......................................28
- 17 APPENDICIES....................................................25
- 17.1 XML Document Type Definition..................................25
+16 AUTHORS' ADDRESSES.............................................28
+
+17 APPENDICIES....................................................28
+17.1 XML Document Type Definition..................................28
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 3]
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.
+ 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.
+ 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.
In the interests of timeliness, the following set of security
mechanisms are not addressed by this document:
- Clemm, Hopkins, Sedlar, Whitehead [Page 3]
- * Access control that applies only to a particular property on
- a resource, rather than the entire resource,
+ * 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),
+ * 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 the ways an ACL on a resource is initialized,
* Specification of an ACL that applies globally to a method,
rather than to a particular resource.
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 (Section 6.2), and principals required
to be present in an ACE (Section 6.3). 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.
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 4]
Internationalization considerations (Section 9) and security
- considerations (Section 10) round out the specification. An appendix
- (Section 17.1) provides an XML Document Type Definition (DTD) for
- the XML elements defined in the specification.
+ considerations (Section 10) round out the specification. An
+ appendix (Section 17.1) 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.
+ 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.
+ An "aggregate privilege" is a privilege that contains a set of
+ other privileges.
abstract privilege
- Clemm, Hopkins, Sedlar, Whitehead [Page 4]
The modifier "abstract", when applied to an atomic or aggregate
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.
inherited ace
An "inherited ace" is an ace that is shared from the acl of another
resource.
+Clemm, Hopkins, Sedlar, Whitehead [Page 5]
+
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].
+ "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
+ this document are to be interpreted as described in [RFC2119].
2 PRINCIPALS
- A principal is an HTTP 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. Although
- an implementation MAY support PROPFIND and PROPPATCH to access and
- modify information about a principal, it is not required to do so.
+ 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 URL of
+ any scheme MAY be used to identify a principal resource. However,
+ servers implementing this specification SHOULD 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. Although an implementation SHOULD support PROPFIND
+ and 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. A collection
principal may only contain other principals (not other types of
resources). Servers that support aggregation of principals (e.g.
groups of users or other groups) MUST manifest them as collection
principals. The WebDAV methods for examining and maintaining
collections (e.g. DELETE, PROPFIND) MAY be used to maintain
collection principals. Membership in a collection principal is
recursive, so a principal in a collection principal GRPA contained
by collection principal 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.
3 PRIVILEGES
- Ability to perform a given method on a resource SHOULD be controlled
- by one or more privileges. Authors of protocol extensions that
-
- Clemm, Hopkins, Sedlar, Whitehead [Page 5]
- 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.
+ 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
+ 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
+ internal member of a collection. Since these privileges control
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 6]
+ 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.
Privileges may have the quality of being abstract, in which case
they cannot be set in an ACE. Aggregate and atomic 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
+ 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
and classify non-abstract privileges.
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, WebDAV defines a set of well-known privileges (e.g.
DAV:read and DAV:write), which can at least be used to classify the
- other privileges defined on a particular resource.
+ other privileges defined on a particular resource. The access
+ permissions on null and lock-null resources are solely those they
+ inherit (if any), and they are not discoverable (i.e., the ACL
+ 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 state of the
resource, such as PUT and PROPPATCH. Note that state modification
-
- Clemm, Hopkins, Sedlar, Whitehead [Page 6]
is also controlled via locking (see section 5.3 of [WEBDAV]), so
- effective write access requires that both write privileges and write
- locking requirements are satisfied.
+ effective write access requires that both write privileges and
+ write locking requirements are satisfied.
+Clemm, Hopkins, Sedlar, Whitehead [Page 7]
+
3.3 DAV:read-acl Privilege
The DAV:read-acl privilege controls the use of PROPFIND to retrieve
- the DAV:acl, and DAV:current-user-privilege-set properties of the
- resource.
+ the DAV:acl property of the resource.
- 3.4 DAV:write-acl Privilege
+3.4 DAV:read-cuprivset Privilege
- The DAV:write-acl privilege controls use of the ACL method to modify
- the DAV:acl property of the resource.
+ The DAV:read-cuprivset 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.
- 3.5 DAV:all Privilege
+3.6 DAV:all Privilege
DAV:all is an aggregate privilege that contains all privileges on
the resource.
4 PRINCIPAL PROPERTIES
- Principals are manifested to clients as an HTTP resource, identified
- by a URL. A principal MUST have a DAV:displayname property. This
- protocol defines the following additional properties for a
- principal.
+ Principals are manifested to clients as an HTTP resource,
+ identified by a URL. A principal MUST have a DAV:displayname
+ property. This protocol defines the following additional
+ properties for a principal. The name and value of these properties
+ SHOULD NOT be returned by PROPFIND allprop request (as defined in
+ Section 12.14.1 of [RFC2518]). In the descriptions below, a read-
+ only property is defined as a property that MUST NOT be writeable
+ using PROPPATCH.
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 8]
4.1 DAV:is-principal
- This property indicates whether this resource is a principal. A
- resource MUST have a non-empty DAV:is-principal property if and only
- if it is a principal resource. (Note: If we can just add a
- DAV:principal element to the DAV:resourcetype property, then we do
- not need a DAV:is-principal property.)
+ This is a read-only property that indicates whether this resource
+ is a principal. A resource MUST have a non-empty DAV:is-principal
+ property if and only if it is a principal resource.
- PCDATA value: any non-empty value ("T" is suggested)
+ PCDATA value: "true" - resource is a principal, "false" - resource
+ is not a principal (note that in cases where the "F" value might be
+ used, this specification requires the property not be present at
+ all).
- 4.2 DAV:authentication-id
+4.2 DAV:alternate-URL
- A property containing the name used to authenticate this principal
- (typically typed into a login prompt/dialog).
+ This read-only property, if present, contains the URL of a network
+ resource with additional descriptive information about the
+ principal. This property identifies one or more additional network
+ resources (i.e., it contains one or more URLs) 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 OPTIONAL.
-
- PCDATA value: any string
+
- Clemm, Hopkins, Sedlar, Whitehead [Page 7]
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. Some access
control properties (such as DAV:owner) MAY be updated with the
- PROPPATCH method.
+ PROPPATCH method. In the descriptions below, a read-only property
+ is defined as a property that MUST NOT be writeable using
+ PROPPATCH. Since it is expensive, for many servers, to retrieve
+ access 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:
+ 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 property identifies a particular principal as being the "owner"
- of the resource.
+ This 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 write-ACL privilege), clients might display the resource
+ owner in their user interface.
+Clemm, Hopkins, Sedlar, Whitehead [Page 9]
An implementation MAY include a list of selected properties of that
principal resource. Which properties (if any) are included is
- implementation defined. An implementation MAY allow the use of
- PROPPATCH to update the DAV:owner field.
+ implementation defined, but might reasonably include properties
+ such as DAV:displayname, which is useful for the construction of
+ access control user interfaces on the client. A server might
+ support this capability if it wished to save the client the
+ additional network round-trip delay required to retrieve this
+ information using a PROPFIND request on the principal URL in the
+ href element. Servers that do not directly support PROPFIND on
+ principal resources might also support this feature, since it
+ allows them to return a server-controlled subset of the properties
+ on the principal resource.
+
+ An implementation MAY allow the use of PROPPATCH to update the
+ DAV:owner field. If the DAV:owner property is writeable, clients
+ MUST NOT submit the prop element; only the href element can be
+ modified by the client. The purpose of this restriction is to limit
+ the scope of effect of a PROPPATCH to just the owner property's
+ resource; setting the prop element would additionally require
+ modification to properties of the principal resource identified by
+ the href element.
5.2 DAV:supported-privilege-set
This is a read-only 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.
+ 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.
+ 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
+ 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
- Clemm, Hopkins, Sedlar, Whitehead [Page 8]
- privilege tree also serves to hide complexity in implementations
- allowing large number of privileges to be defined by displaying
- aggregates to the user.
+Clemm, Hopkins, Sedlar, Whitehead [Page 10]
+ 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.
5.3 DAV:current-user-privilege-set
DAV:current-user-privilege-set is a read-only property containing
the exact set of privileges (as computed by the server) granted to
- the currently authenticated HTTP user. A user-agent can use the
+ 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 determine what operations
- can be performed by the current principal, without having to
+ 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.
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 privilege from the DAV:supported-
- privilege-set property.
+ 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.
5.4 DAV:acl
- This property specifies the list of access control entries (ACEs),
- which define what principals are to get what privileges for this
- resource.
+ This is a read-only 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.
+ granted or denied to a single principal. If the DAV:acl property
+ is empty, no principal is granted any privilege.
- An attempt to update the DAV:acl property with a PROPPATCH MUST
- fail.
-
5.4.1 ACE Principal
- The DAV:principal element identifies the principal to which this ACE
- applies.
+ 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
-
- Clemm, Hopkins, Sedlar, Whitehead [Page 9]
- contained by that DAV:href. An implementation MAY include a
- DAV:prop element after the DAV:href element, containing a list of
- selected properties of that principal resource. Which properties
- (if any) are included in the DAV:prop element is implementation
- defined. The DAV:prop element is primarily intended for
- implementations that do not support PROPFIND requests on the
- principal URL.
+Clemm, Hopkins, Sedlar, Whitehead [Page 11]
+ 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. An implementation
+ MAY include a DAV:prop element after the DAV:href element,
+ containing a list of selected properties of that principal
+ resource. Which properties (if any) are included in the DAV:prop
+ element is implementation defined. The DAV:prop element can be used
+ by servers that do not support PROPFIND requests on principal
+ resources to return principal-related information (such as the
+ value of the DAV:displayname property) that a client would find
+ useful in the creation of an access control user interface. A
+ server might also support this capability if it wished to save the
+ client the additional network round-trip delays required to
+ retrieve this information via a series of PROPFIND requests on each
+ principal URL in the ACL. In the worst case, this is one additional
+ PROPFIND per ACE.
The current user always matches DAV:all.
The current user matches DAV:authenticated only if authenticated.
@@ -530,105 +611,111 @@
resource contains a DAV:href that 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.
+ resource only if that resource is a principal object and the
+ current user is authenticated as being that principal.
+Clemm, Hopkins, Sedlar, Whitehead [Page 12]
+
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 elements specified in the DAV:supported-privilege-set of
- that resource.
+ 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.
- Clemm, Hopkins, Sedlar, Whitehead [Page 10]
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.
+ modified directly, but instead the ACL on the resource from which
+ it is inherited must be modified.
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.
5.5 DAV:acl-semantics
This is a read-only 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.
+ 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 could use this property to determine exactly,
+ 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.
+Clemm, Hopkins, Sedlar, Whitehead [Page 13]
+
5.6 DAV:principal-collection-set
This read-only property contains zero, one, or more URLs that
- identify a collection principal. It is expected that implementations
- of this protocol will typically employ 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 collection hierarchy containing multiple principals and
- collection principals. An access control protocol user agent could
- use the contents of DAV:principal-collection-set to, for example,
- 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.
+ identify a collection principal. It is expected that
+ implementations of this protocol will typically employ 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 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.
- Clemm, Hopkins, Sedlar, Whitehead [Page 11]
-
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 are not
- limited to http scheme URLs, and can, for example, be ldap 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.
+ 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.
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.
>> Request <<
@@ -642,36 +729,35 @@
uri="/top/container/", response="...", opaque="..."
+Clemm, Hopkins, Sedlar, Whitehead [Page 14]
>> Response <<
HTTP/1.1 207 Multi-Status
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
+ xmlns:A="http://www.webdav.org/acl/">
HTTP/1.1 200 OK
http://www.foo.org/users/gclemm
-
- Clemm, Hopkins, Sedlar, Whitehead [Page 12]
Any operation
Read any object
@@ -697,38 +783,37 @@
Write the ACL
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 15]
http://www.foo.org/users/esedlar
- esedlar
Eric Sedlar
-
- Clemm, Hopkins, Sedlar, Whitehead [Page 13]
http://www.foo.org/groups/marketing/
@@ -737,119 +822,125 @@
http://www.foo.org/top/
- 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: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:acl (aggregate, abstract)
+ DAV:all (aggregate, abstract)
|
+-- DAV:read
+-- DAV:write (aggregate, abstract)
|
- +-- http://www.acl.org/create
- +-- http://www.acl.org/update
- +-- http://www.acl.org/delete
+ +-- http://www.webdav.org/acl/create
+ +-- http://www.webdav.org/acl/update
+ +-- http://www.webdav.org/acl/delete
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 16]
+-- 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: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.
+ 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.
- Clemm, Hopkins, Sedlar, Whitehead [Page 14]
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.
+ 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.
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.
+ principal*)>
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.
+ 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.
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 17]
+ (first-match | all-grant-before-any-deny | specific-deny-
+ overrides-grant)>
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.
+ 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.
+ 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:no-deny 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
+6.1.3 DAV:specific-deny-overrides-grant ACE Combination
- Clemm, Hopkins, Sedlar, Whitehead [Page 15]
- 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.
+ 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.
-
+
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
@@ -857,121 +948,135 @@
ACEs.
6.3 Required Principals
The required principal elements identify which principals must have
an ACE defined in the ACL.
+ (href | all | authenticated | unauthenticated | property | self)>
- For example, the following element requires that the ACE contain a
+Clemm, Hopkins, Sedlar, Whitehead [Page 18]
+ For example, the following element requires that the ACL contain a
DAV:owner property ACE:
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.
7.1.1Example - OPTIONS
- >> REQUEST <<
+ >> Request <<
OPTIONS /foo.html HTTP/1.1
Host: www.webdav.org
Content-Length: 0
- Clemm, Hopkins, Sedlar, Whitehead [Page 16]
- >> RESPONSE <<
+ >> 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.
8 ACCESS CONTROL METHODS
8.1 ACL
- A DAV:acl property of a resource is modified by the ACL method. A
- new DAV:acl value must be written in its entirety, including any
+ The ACL method modifies the DAV:acl property of a resource. A new
+ DAV:acl value must be written in its entirety, including any
inherited ACEs. Unless 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. If a server restricts the set of ACEs
visible to the current user via the DAV:acl property, then the ACL
request would only replace the set of ACEs visible to the current
user, and would not affect any ACE that was not visible.
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.
+Clemm, Hopkins, Sedlar, Whitehead [Page 19]
+ When submitting ACEs, clients MUST NOT include the optional prop
+ element (a child of the principal element). The purpose of this
+ restriction is to limit the scope of effect of the ACL method to
+ just the resource identified by the Request-URI; setting the prop
+ element would additionally require property modification for one or
+ more principal resources.
+
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 in the response body.
+ 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 in the response body.
: An implementation MAY protect an ACE from
modification or deletion. For example, some implementations
implicitly grant the DAV:owner of a resource DAV:read-acl and
DAV:write-acl privileges, and this cannot be changed by a client.
- : 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.
+ : 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 ACEs
MUST precede all inherited ACEs.
: All non-inherited deny ACEs MUST
precede all non-inherited grant ACEs.
+ If the following precondition is not met, the server MUST return a
+ 409 (Conflict) response, and the indicated XML element MUST be
+ returned in the response body:
+
+ : Inherited ACEs MUST exist on a parent
+ resource.
+
8.1.2 Example: the ACL method
In the following example, user "fielding", authenticated by
information in the Authorization header, grants the principal
-
- Clemm, Hopkins, Sedlar, Whitehead [Page 17]
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 inherited from the parent collection
+ resource read-acl and write-acl privileges, and grants everyone
+ read privileges inherited from the parent collection
http://www.foo.bar/top/.
>> 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="...",
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 20]
uri="/top/container/", response="...", opaque="..."
http://www.foo.org/users/esedlar
@@ -994,37 +1099,40 @@
>> Response <<
HTTP/1.1 200 OK
8.1.3 Example: ACL method failure due to omission of protected ACE
In the following request, user "fielding", authenticated by
information in the Authorization header, attempts to grant the
principal identified by the URL http://www.foo.org/users/esedlar
- (i.e., the user "esedlar") read privileges, but fails because an
- protected ACE has been omitted (e.g. the ACE granting the DAV:owner
- DAV:read-acl and DAV:write-acl privileges must always be present
- since it is protected -- see Section 5.4.3).
+ (i.e., the user "esedlar") read 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-acl and DAV:write-
+ acl privileges. The ACL method invocation fails because this
+ protected ACE is omitted, thus violating the semantics of ACE
+ protection..
- Clemm, Hopkins, Sedlar, Whitehead [Page 18]
>> 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="..."
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 21]
http://www.foo.org/users/esedlar
@@ -1034,52 +1142,53 @@
Content-Type: text/xml; charset="utf-8"
Content-Length: xxx
8.1.4 Example: ACL method failure due to inherited ACEs preceding non-
inherited ACEs
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.
+ 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 add a third ACE, granting the principal
identified by the URL http://www.foo.org/users/gclemm (i.e., the
- user "gclemm") DAV:write permission, but in the request places the
+ user ôgclemmö) DAV:write permission, but in the request places the
inherited ACEs before the non-inherited ACEs, causing an error on
this specific server implementation. Note that on a different
implementation, this request might be accepted.
>> Request <<
- Clemm, Hopkins, Sedlar, Whitehead [Page 19]
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",
realm="users@foo.org", nonce="...",
uri="/top/index.html", response="...", opaque="..."
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 22]
http://www.foo.org/users/ejw
@@ -1098,47 +1207,46 @@
>> 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.
+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
+ 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
-
- Clemm, Hopkins, Sedlar, Whitehead [Page 20]
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",
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 23]
realm="users@foo.org", nonce="...",
- uri="/diamond/engagement-ring.gif", response="...",
- opaque="..."
+ uri="/diamond/engagement-ring.gif", response="...", opaque="..."
http://www.foo.org/users/friends/
http://www.foo.org/users/ygoland-so
@@ -1152,212 +1260,213 @@
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 INTERNATIONALIZATION CONSIDERATIONS
In this specification, the only human-readable content can be found
- in the DAV:authentication-id property, found on principal resources.
- This property contains the name used to authenticate a principal,
- typically by a user entering this name into a password entry screen.
- As a result, the authentication-id must be capable of representing
- names in multiple character sets. Since DAV:authentication-id is 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.
+ 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.
- Clemm, Hopkins, Sedlar, Whitehead [Page 21]
- For properties other than DAV:authentication-id, it is expected that
- implementations will treat the property names and values as tokens,
- and convert these tokens 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.
+ 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 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.
+Clemm, Hopkins, Sedlar, Whitehead [Page 24]
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.
+ 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].
+ described in the WebDAV Distributed Authoring protocol
+ specification [RFC2518].
10 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.
+ 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.
10.1 Increased Risk of Compromised Users
In the absence of a mechanism for remotely manipulating access
- control specifications, 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.
-
- 10.2 Authentication-id Property and Dictionary Attacks
-
- Every principal has a DAV:authentication-id property defined on it,
- which provides the name used to authenticate this principal,
- typically the username portion of a username/password authentication
- scheme. An attacker can use the information in this property when
- attempting either a brute-force, or a dictionary attack to guess the
- principal's identifying password. By providing the username in
- DAV:authentication-id, the scope of an attack can be reduced to a
- single, valid username. Furthermore, it is possible that principals
- can potentially belong to a collection. In this case, it is possible
- to use the PROPFIND method to retrieve the DAV:authentication-id
- property from all of the principals in a collection, thus providing
- multiple usernames that can be the focus of attack.
-
- Clemm, Hopkins, Sedlar, Whitehead [Page 22]
- To reduce this risk, the DAV:authentication-id property should not
- be world-readable. Which principals are granted default read
- privilege for DAV:authentication-id should be carefully considered
- in any deployment of this protocol.
+ 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.
- 10.3 Risks of the read-acl Privilege
+10.2 Risks of the read-acl and cuprivset 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 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,
+ 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 privileges
- for authenticated principals should be carefully analyzed when
- deploying this protocol.
+ unauthenticated principals, and restrictions on read-acl and
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 25]
+ 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.
11 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].
12 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.
+ elements. All other IANA considerations mentioned in [RFC2518]
+ also applicable to WebDAV ACL.
13 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
+ 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
-
- Clemm, Hopkins, Sedlar, Whitehead [Page 23]
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.
+ this standard. Please address the information to the IETF
+ Executive Director.
14 ACKNOWLEDGEMENTS
This protocol is the collaborative product of the WebDAV ACL design
team: Bernard Chester, Geoff Clemm (Rational), Anne Hopkins
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 26]
(Microsoft), Barry Lind (Xythos), Sean Lyndersay (Microsoft), Eric
Sedlar (Oracle), Greg Stein (Apache.org), and Jim Whitehead (UC
Santa Cruz). The authors are grateful for the detailed review and
comments provided by Jim Amsden, Gino Basso, Murthy Chintalapati,
- Dennis Hamilton, Ron Jacobs, Chris Knight, and Remy Maucherat. 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.
+ Dennis Hamilton, Laurie Harper, Ron Jacobs, Chris Knight, and Remy
+ Maucherat. 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.
15 REFERENCES
15.1 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.
+ 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.
+ 3023. IBM Tokyo Research Laboratory, simonstl.com, Skymoon
+ Ventures, January, 2001.
- Clemm, Hopkins, Sedlar, Whitehead [Page 24]
[UTF-8] F. Yergeau, "UTF-8, a transformation format of Unicode and
ISO 10646." RFC 2279. Alis Technologies. January, 1998.
+Clemm, Hopkins, Sedlar, Whitehead [Page 27]
+
15.2Informational References
- [RFC2026] S.Bradner, "The Internet Standards Process û Revision 3."
+ [RFC2026] S.Bradner, "The Internet Standards Process -- Revision 3."
RFC 2026, BCP 9. Harvard, October, 1996.
16 AUTHORS' ADDRESSES
Geoffrey Clemm
Rational Software
20 Maguire Road
Lexington, MA 02421
Email: geoffrey.clemm@rational.com
@@ -1383,29 +1492,31 @@
17 APPENDICIES
17.1XML Document Type Definition
+
- Clemm, Hopkins, Sedlar, Whitehead [Page 25]
-
+
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 28]
@@ -1440,39 +1551,42 @@
- Clemm, Hopkins, Sedlar, Whitehead [Page 26]
+Clemm, Hopkins, Sedlar, Whitehead [Page 29]
+ principal*)>
+ (first-match | all-grant-before-any-deny | specific-deny-
+ overrides-grant)>
-
+
+ (href | all | authenticated | unauthenticated | property | self)>
+
+
+Clemm, Hopkins, Sedlar, Whitehead [Page 30]