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INTERNET-DRAFT                                                  K. Ito
Expires April, 2002                                      October, 2001

          Ticket-Based Access Control Extension to WebDAV


Status of this Memo

   This document is an Internet-Draft and is subject to 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 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

   The list of Internet-Draft Shadow Directories can be accessed at


   This draft describes an extension to the WebDAV Distributed
   Authoring Protocol which provides a mechanism for transferring
   access privileges on a DAV resource through the use of a token
   shared between multiple principals. This allows a principal to
   transfer specific privileges to others in a time or usage-limited

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",
   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].

1.  Overview

   Tickets are a mechanism for the transfer of specific access

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   privileges for a limited time or number of uses from one principal
   to another.

   Issuing a ticket on a resource provides a principal with a ticket
   identifier, a token which can then be distributed to other
   principals. A principal who presents this ticket ID transfers
   access privileges from the original principal to himself. This can
   be useful in situations where one wishes to grant access to
   individuals who are not easily defined within the access control
   scheme implemented by the server, for example, individuals who do
   not have accounts on the server on which the resource resides. It
   can also be used if a principal wishes to grant duration or usage
   limited access on a specific resource to other users.

   In any series of transactions involving tickets, there are two roles
   played by one or more principals. The first role is that of the
   principal who "issues" the ticket by sending a MKTICKET request to
   the server, and receives a ticket in the response. This user will be
   referred to as the "ticket owner". The second role is that of the
   principal who "uses" the ticket, by sending the ticket as a
   parameter in another WebDAV request to gain access to the resource.
   This principal will be referred to as the "ticket user". Note that
   it is possible for both roles to be played by the same principal,
   and for multiple distinct principals to play the ticket user role
   on the same ticket.

1.1 Transfer of access privileges

   Every ticket MUST define a set of permissions which it will pass
   from the ticket owner to the ticket user. This set of permissions
   acts as a mask on the resource permissions. Permissions that the
   ticket grants on a resource, but which the ticket owner has not been
   granted will not be granted to the ticket user. Similarly,
   permissions that the ticket owner has been granted on a resource,
   but which the ticket does not grant will not be granted to the
   ticket user.

1.2 Ticket ID Scheme

   The only condition imposed on ticket IDs is that the ticket ID MUST
   be unique on a resource at any given time. However, since the ticket
   ID is used as proof that a principal is in possession of the ticket,
   a server SHOULD select a ticket ID scheme such that it would be
   sufficiently difficult for an adversary in a way to guess or predict
   a ticket ID.

1.3 Ticket Use

   A ticket can be presented to the server either as a header in the
   request for a resource or as a parameter in the query component
   of the Request-URI as described in [RFC2396]. Allowing the ticket
   to be presented in the URI makes it possible for a ticketed resource

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   to be accessed using the ticket with a single HTML link. When
   presented in the query component, the ticket ID should be given as
   the value of the "ticket" parameter. When presented as a header, the
   ticket ID should be given as the value of the "Ticket" header.

1.4 Ticket Invalidation

   A ticket can be invalidated in one of three ways, any of which is
   sufficient to invalidate the ticket: (1) The ticket times out by
   existing for longer than the timeout interval determined at ticket
   creation, (2) the ticket is used to gain access to a resource more
   times than were specified at ticket creation, (3) the ticket is
   deleted using the DELTICKET method. In any of these three cases, the
   server MUST treat any further requests using the invalidated ticket
   as though the ticket did not exist.

1.5 Ticket Discovery

   In order for client to determine the tickets that have been issued
   on a resource, the ticketdiscovery property is provided. The
   ticketdiscovery property lists all active tickets, their ticket ID's,
   the time remaining on each ticket, the number of uses remaining on
   each ticket, the permissions granted by each ticket, and the ticket
   owner. Any resource that supports the MKTICKET method MUST support
   the ticketdiscovery property.

   As the ability to view a ticket's ID also gives the viewer the
   ability to use the ticket, servers SHOULD restrict the visibility of
   the ticketdiscovery property to principals that it has determined to
   have sufficient access privileges on the resource.

2. The MKTICKET Method

   The following describes the MKTICKET method, which is used to
   request a ticket on a URI.

2.1.  Operation

   A MKTICKET request creates a ticket on the resource specified in the
   Request-URI. MKTICKET requests MUST have an XML request body which
   contains a ticketinfo XML element (see section 4 for XML tag
   definitions). The ticketinfo element contains subelements specifying
   how long the ticket is valid for, how many times the ticket may be
   used, and the permissions that the ticket transfers to the ticket

   The response MUST contain the value of the resource's
   ticketdiscovery property in a prop XML element.

   In order to indicate the ID associated with a newly created ticket,
   a Ticket response header containing the newly created ticket's ID
   MUST be included in the response for every successful MKTICKET

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2.2.  Status Codes

   200 (OK) - The MKTICKET request succeeded and the value of the
   ticketdiscovery property for this resource is included in the body.

   400 (Bad Request) - The XML body was omitted or not parsable.

   403 (Forbidden) - The user does not have proper access privileges on
   this resource.

   404 (Not Found) - The resource specified could not be found.

2.3.  Example - Ticket request

   MKTICKET /test.txt HTTP/1.1
   Host: www.foo.com
   Content-length: xxx
   Content-Type: text/xml; charset="utf-8"
   Authorization: Basic dGVzdHVzZXI6dGVzdHVzZXI=

   <?xml version="1.0" encoding="utf-8" ?>
   <D:ticketinfo xmlns:D="DAV:" >

   HTTP/1.0 200 OK
   Ticket: A658B29924F9D39C
   Content-Type: text/xml; charset=UTF-8
   Content-Length: xxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:prop xmlns:D="DAV:">

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   This example shows the successful creation of a one-time use ticket
   with a lifetime of one hour on the resource
   http://www.foo.com/test.txt. Since the ticket was requested by the
   principal identified by "http://www.foo.com/users/testuser", the
   ticket owner is listed as such. The ticket ID, listed both in the
   ticketdiscovery property and the Ticket header displays the ID
   assigned to this ticket, in this case a random 64-bit integer
   expressed in hexadecimal notation.

2.4.  Example - Using a ticket

   GET /test.txt?ticket=A658B29924F9D39C HTTP/1.1
   Host: www.foo.com

   HTTP/1.0 200 OK
   Content-Type: text/plain
   Content-Length: xxx

   <content follows>

   In this example, it is assumed that the ticket with ID
   A658B29924F9D39C is the ticket requested in example 2.3, and that it
   was valid at the time of use. It is also assumed that the principal
   http://www.foo.com/users/testuser who issued the ticket has read
   access privileges on the resource. Since the ticket grants read
   access, and since the ticket owner has read access on the resource,
   the request succeeds.

3. The DELTICKET Method

   The DELTICKET method is used to delete a ticket on a resource. To
   identify the ticket that is to be deleted, the "Ticket" header MUST
   be passed with the DELTICKET request. Any resource which supports
   the MKTICKET method must also support the DELTICKET method.

3.1.  Status Codes

   204 (No Content) - The DELTICKET request succeeded; the ticket
   specified has been deleted.

   404 (Not Found) - The resource specified could not be found.

   412 (Precondition Failed) - The ticket specified does not exist.

3.2.  Example - Ticket deletion

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   DELTICKET /test.txt HTTP/1.1
   Host: www.foo.com
   Ticket: A658B29924F9D39C

   HTTP/1.1 204 No Content

4.  XML Element Definitions

4.1.  Previously defined XML elements

   This draft makes use of a number of XML elements that have
   previously been defined in other documents. DAV:href,
   DAV:multistatus, DAV:prop, DAV:propfind, DAV:propstat, DAV:response
   and DAV:status are defined in the WebDAV Distributed Authoring
   Protocol [RFC2518].  DAV:owner, DAV:privilege, DAV:read, and
   DAV:write are defined in the WebDAV Access Control Protocol [WACP]
   internet draft. To avoid a dependency on that draft, the relevant
   definitions are reproduced in section 5 of this document.

4.2.  ticketdiscovery property
      Describes the tickets currently valid on a resource
     The ticketdiscovery property returns a listing of all valid
   tickets on a resource. The server is free to withhold any or all of
   this information if the requesting principal does not have sufficient
   access privileges to see the data.

   <!ELEMENT ticketdiscovery (ticket)*>

4.2.1.  Example - Retrieving the ticketdiscovery Property

   PROPFIND /test.txt HTTP/1.1
   Host: www.foo.com
   Content-type: text/xml; charset=UTF-8
   Content-length: xxx
   Authorization: Basic dGVzdHVzZXI6dGVzdHVzZXI=

   <?xml version="1.0" encoding="utf-8" ?>
   <D:propfind xmlns:D="DAV:">

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   HTTP/1.0 207 MultiPart Response
   Content-Type: text/xml; charset=UTF-8
   Content-Length: xxxx

   <?xml version="1.0" encoding="utf-8" ?>
   <D:multistatus xmlns:D="DAV:">

         <D:status>HTTP/1.1 200 OK</D:status>

   The request above is for the ticketdiscovery property on the
   resource http://www.foo.com/test.txt.  Two tickets that are active
   on this resource are returned. Note that there may be more tickets
   defined on this resource, but the requesting user may not have
   permission to view them.

4.3.  ticketinfo XML Element

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      Describes a single ticket
      Contains relevant information about a ticket, including the
   ticket ID, the owner of the ticket, the amount of time remaining
   before the ticket expires, the number of visits the ticket can be
   used for before it expires, and the access privileges defined on the
   The ticketinfo element is used both in the MKTICKET request and as a
   child of the ticketdiscovery property in a PROPFIND request. The id
   and owner elements should be omitted in a MKTICKET request since the
   server is responsible for setting both of these properties of the

   <!ELEMENT ticketinfo (id?, owner?, timeout, visits, privilege)>

4.4.  id XML Element
      Contains the ID of a ticket. See section 1.2 for recommendations
   on generating the ticket ID.

   <!ELEMENT id (#PCDATA)>

4.5.  visits XML Element

      Describes the number of visits that the ticket has remaining on
      1*DIGIT | "infinity"

   <!ELEMENT visits (#PCDATA)>

5. Definitions From ACL Draft

   This draft makes use of a number of terms and XML property tags that
   are defined in the internet draft "WebDAV Access Control Protocol"
   [WACP]. To avoid making this draft dependent on [WACP], the

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   following definitions have been copied verbatim from that document,
   with portions not used in this draft omitted.

5.1 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. 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 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.

5.2 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.

5.2.1 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

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   privilege MAY control the OPTIONS method.

   <!ELEMENT read EMPTY>

5.2.2 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 [RFC2518]), so
   effective write access requires that both write privileges and write
   locking requirements are satisfied.

   <!ELEMENT write EMPTY>

5.3 Access Control Properties

5.3.1 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.

   <!ELEMENT owner (href)>

6. Security Considerations

   By providing another means for granting access privileges on
   resources, tickets increase the risk of unauthorized access to the
   particular resources that they are issued on. Since the ticket ID is
   sent in both the response from the server following a MKTICKET
   request and in the request for a resource using the ticket, there
   is the risk of the ticket ID being intercepted by an attacker who
   can then present it to the server and use it to maliciously gain
   access to the resource on which the ticket is issued.

   However, this risk is mitigated by several factors. First, as long
   as the channels used to request, distribute, and use the ticket are
   secure, there is no added risk in using tickets. Second, since a
   ticket transfers a limited set of access privileges on a single
   resource for a limited duration and limited number of accesses,
   the scope of potential security violations is limited.

7. References

   [RFC2396] T. Berners-Lee, R. Fielding, L. Masinter, "Uniform
   Resource Identifiers (URI): Generic Syntax", RFC 2396. MIT/LCS,

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   U.C. Irvine, Xerox, August, 1998.

   [RFC2026] S.Bradner, "The Internet Standards Process - Revision 3."
   RFC 2026, BCP 9. Harvard, October, 1996.

   [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.

   [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.

   [WACP] G. Clemm, A. Hopkins, E. Sedlar, J. Whitehead, "WebDAV Access
   Control Protocol." IETF Internet Draft draft-ietf-webdav-acl-06.
   Rational, Microsoft, Oracle, U.C. Santa Cruz, June, 2001.

8. Author's Address

   Keith Ito
   77 Maiden Lane, Suite 200
   San Francisco, CA, USA

This internet draft expires April, 2002.

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