LinuxDig.com Request For Comments

RFC Number : 3744 Title : Web Distributed Authoring and Versioning (WebDAV) Access Control Protocol. Network Working Group G. Clemm Request for Comments: 3744 IBM Category: Standards Track J. Reschke greenbytes E. Sedlar Oracle Corporation J. Whitehead U.C. Santa Cruz May 2004 Web Distributed Authoring and Versioning (WebDAV) Access Control Protocol Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the 'Internet Official Protocol Standards' (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document specifies a set of methods, headers, message bodies, properties, and reports that define Access Control extensions to the WebDAV Distributed Authoring Protocol. This protocol permits a client to read and modify access control lists that instruct a server whether to allow or deny operations upon a resource (such as HyperText Transfer Protocol (HTTP) method invocations) by a given principal. A lightweight representation of principals as Web resources supports integration of a wide range of user management repositories. Search operations allow discovery and manipulation of principals using human names. Clemm, et al. Standards Track [Page 1]  RFC 3744 WebDAV Access Control Protocol May 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Terms. . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.2. Notational Conventions . . . . . . . . . . . . . . . . . 8 2. Principals . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. Privileges . . . . . . . . . . . . . . . . . . . . . . . . . . 8 3.1. DAV:read Privilege . . . . . . . . . . . . . . . . . . . 10 3.2. DAV:write Privilege. . . . . . . . . . . . . . . . . . . 10 3.3. DAV:write-properties Privilege . . . . . . . . . . . . . 10 3.4. DAV:write-content Privilege. . . . . . . . . . . . . . . 11 3.5. DAV:unlock Privilege . . . . . . . . . . . . . . . . . . 11 3.6. DAV:read-acl Privilege . . . . . . . . . . . . . . . . . 11 3.7. DAV:read-current-user-privilege-set Privilege. . . . . . 12 3.8. DAV:write-acl Privilege. . . . . . . . . . . . . . . . . 12 3.9. DAV:bind Privilege . . . . . . . . . . . . . . . . . . . 12 3.10. DAV:unbind Privilege . . . . . . . . . . . . . . . . . . 12 3.11. DAV:all Privilege. . . . . . . . . . . . . . . . . . . . 13 3.12. Aggregation of Predefined Privileges . . . . . . . . . . 13 4. Principal Properties . . . . . . . . . . . . . . . . . . . . . 13 4.1. DAV:alternate-URI-set. . . . . . . . . . . . . . . . . . 14 4.2. DAV:principal-URL. . . . . . . . . . . . . . . . . . . . 14 4.3. DAV:group-member-set . . . . . . . . . . . . . . . . . . 14 4.4. DAV:group-membership . . . . . . . . . . . . . . . . . . 14 5. Access Control Properties. . . . . . . . . . . . . . . . . . . 15 5.1. DAV:owner. . . . . . . . . . . . . . . . . . . . . . . . 15 5.1.1. Example: Retrieving DAV:owner . . . . . . . . . . 15 5.1.2. Example: An Attempt to Set DAV:owner. . . . . . . 16 5.2. DAV:group. . . . . . . . . . . . . . . . . . . . . . . . 18 5.3. DAV:supported-privilege-set. . . . . . . . . . . . . . . 18 5.3.1. Example: Retrieving a List of Privileges Supported on a Resource . . . . . . . . . . . . . 19 5.4. DAV:current-user-privilege-set . . . . . . . . . . . . . 21 5.4.1. Example: Retrieving the User's Current Set of Assigned Privileges . . . . . . . . . . . . . . . 22 5.5. DAV:acl. . . . . . . . . . . . . . . . . . . . . . . . . 23 5.5.1. ACE Principal . . . . . . . . . . . . . . . . . . 23 5.5.2. ACE Grant and Deny. . . . . . . . . . . . . . . . 25 5.5.3. ACE Protection. . . . . . . . . . . . . . . . . . 25 5.5.4. ACE Inheritance . . . . . . . . . . . . . . . . . 25 5.5.5. Example: Retrieving a Resource's Access Control List. . . . . . . . . . . . . . . . . . . . . . . 25 5.6. DAV:acl-restrictions . . . . . . . . . . . . . . . . . . 27 5.6.1. DAV:grant-only. . . . . . . . . . . . . . . . . . 27 5.6.2. DAV:no-invert ACE Constraint. . . . . . . . . . . 28 5.6.3. DAV:deny-before-grant . . . . . . . . . . . . . . 28 5.6.4. Required Principals . . . . . . . . . . . . . . . 28 5.6.5. Example: Retrieving DAV:acl-restrictions. . . . . 28 Clemm, et al. Standards Track [Page 2]  RFC 3744 WebDAV Access Control Protocol May 2004 5.7. DAV:inherited-acl-set. . . . . . . . . . . . . . . . . . 29 5.8. DAV:principal-collection-set . . . . . . . . . . . . . . 30 5.8.1. Example: Retrieving DAV:principal-collection-set. 30 5.9. Example: PROPFIND to retrieve access control properties. 32 6. ACL Evaluation . . . . . . . . . . . . . . . . . . . . . . . . 36 7. Access Control and existing methods. . . . . . . . . . . . . . 37 7.1. Any HTTP method. . . . . . . . . . . . . . . . . . . . . 37 7.1.1. Error Handling. . . . . . . . . . . . . . . . . . 37 7.2. OPTIONS. . . . . . . . . . . . . . . . . . . . . . . . . 38 7.2.1. Example - OPTIONS . . . . . . . . . . . . . . . . 39 7.3. MOVE . . . . . . . . . . . . . . . . . . . . . . . . . . 39 7.4. COPY . . . . . . . . . . . . . . . . . . . . . . . . . . 39 7.5. LOCK . . . . . . . . . . . . . . . . . . . . . . . . . . 39 8. Access Control Methods . . . . . . . . . . . . . . . . . . . . 40 8.1. ACL. . . . . . . . . . . . . . . . . . . . . . . . . . . 40 8.1.1. ACL Preconditions . . . . . . . . . . . . . . . . 40 8.1.2. Example: the ACL method . . . . . . . . . . . . . 42 8.1.3. Example: ACL method failure due to protected ACE conflict. . . . . . . . . . . . . . . . . . . 43 8.1.4. Example: ACL method failure due to an inherited ACE conflict. . . . . . . . . . . . . . 44 8.1.5. Example: ACL method failure due to an attempt to set grant and deny in a single ACE . . . . . . 45 9. Access Control Reports . . . . . . . . . . . . . . . . . . . . 46 9.1. REPORT Method. . . . . . . . . . . . . . . . . . . . . . 46 9.2. DAV:acl-principal-prop-set Report. . . . . . . . . . . . 47 9.2.1. Example: DAV:acl-principal-prop-set Report. . . . 48 9.3. DAV:principal-match REPORT . . . . . . . . . . . . . . . 49 9.3.1. Example: DAV:principal-match REPORT . . . . . . . 50 9.4. DAV:principal-property-search REPORT . . . . . . . . . . 51 9.4.1. Matching. . . . . . . . . . . . . . . . . . . . . 53 9.4.2. Example: successful DAV:principal-property-search REPORT. . . . . . . . . . . . . . . . . . . . . . 54 9.5. DAV:principal-search-property-set REPORT . . . . . . . . 56 9.5.1. Example: DAV:principal-search-property-set REPORT. . . . . . . . . . . . . . . . . . . . . . 58 10. XML Processing . . . . . . . . . . . . . . . . . . . . . . . . 59 11. Internationalization Considerations. . . . . . . . . . . . . . 59 12. Security Considerations. . . . . . . . . . . . . . . . . . . . 60 12.1. Increased Risk of Compromised Users. . . . . . . . . . . 60 12.2. Risks of the DAV:read-acl and DAV:current-user-privilege-set Privileges. . . . . . . . 60 12.3. No Foreknowledge of Initial ACL. . . . . . . . . . . . . 61 13. Authentication . . . . . . . . . . . . . . . . . . . . . . . . 61 14. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 62 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 62 Clemm, et al. Standards Track [Page 3]  RFC 3744 WebDAV Access Control Protocol May 2004 16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 62 16.1. Normative References . . . . . . . . . . . . . . . . . . 62 16.2. Informative References . . . . . . . . . . . . . . . . . 63 Appendices A. WebDAV XML Document Type Definition Addendum . . . . . . . . . 64 B. WebDAV Method Privilege Table (Normative). . . . . . . . . . . 67 Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 71 Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 72 1. Introduction The goal of the WebDAV access control extensions is to provide an interoperable mechanism for handling discretionary access control for content and metadata managed by 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 what operations you can perform on 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 'operations you can perform' are 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. Since every ACE contains the identifier of a principal, client software operated by a human must provide a mechanism for selecting this principal. This specification uses http(s) scheme URLs to identify principals, which are represented as WebDAV-capable resources. There is no guarantee that the URLs identifying principals will be meaningful to a human. For example, http://www.example.com/u/256432 and http://www.example.com/people/Greg.Stein are both valid URLs that could be used to identify the same principal. To remedy this, every principal resource has the DAV:displayname property containing a human-readable name for the principal. Since a principal can be identified by multiple URLs, it raises the problem of determining exactly which principal is being referenced in a given ACE. It is impossible for a client to determine that an ACE granting the read privilege to http://www.example.com/people/ Greg.Stein also affects the principal at http://www.example.com/u/ 256432. That is, a client has no mechanism for determining that two Clemm, et al. Standards Track [Page 4]  RFC 3744 WebDAV Access Control Protocol May 2004 URLs identify the same principal resource. As a result, this specification requires clients to use just one of the many possible URLs for a principal when creating ACEs. A client can discover which URL to use by retrieving the DAV:principal-URL property (Section 4.2) from a principal resource. No matter which of the principal's URLs is used with PROPFIND, the property always returns the same URL. With a system having hundreds to thousands of principals, the problem arises of how to allow a human operator of client software to select just one of these principals. One approach is to use broad collection hierarchies to spread the principals over a large number of collections, yielding few principals per collection. An example of this is a two level hierarchy with the first level containing 36 collections (a-z, 0-9), and the second level being another 36, creating collections /a/a/, /a/b/, ..., /a/z/, such that a principal with last name 'Stein' would appear at /s/t/Stein. In effect, this pre-computes a common query, search on last name, and encodes it into a hierarchy. The drawback with this scheme is that it handles only a small set of predefined queries, and drilling down through the collection hierarchy adds unnecessary steps (navigate down/up) when the user already knows the principal's name. While organizing principal URLs into a hierarchy is a valid namespace organization, users should not be forced to navigate this hierarchy to select a principal. This specification provides the capability to perform substring searches over a small set of properties on the resources representing principals. This permits searches based on last name, first name, user name, job title, etc. Two separate searches are supported, both via the REPORT method, one to search principal resources (DAV:principal-property-search, Section 9.4), the other to determine which properties may be searched at all (DAV:principal-search- property-set, Section 9.5). Once a principal has been identified in an ACE, a server evaluating that ACE must know the identity of the principal making a protocol request, and must validate that that principal is who they claim to be, a process known as authentication. 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. Clemm, et al. Standards Track [Page 5]  RFC 3744 WebDAV Access Control Protocol May 2004 The following issues are out of scope for this document: o 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, o Role-based security (where a role can be seen as a dynamically defined group of principals), o Specification of the ways an ACL on a resource is initialized, o Specification of an ACL that applies globally to all resources, rather than to a particular resource. o Creation and maintenance of resources representing people or computational agents (principals), and groups of these. This specification is organized as follows. Section 1.1 defines key concepts used throughout the specification, and is followed by a 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 ways ACLs are to be evaluated is described in Section 6. Client discovery of access control capability using OPTIONS is described in Section 7.2. Interactions between access control functionality and existing HTTP and WebDAV methods are described in the remainder of Section 7. The access control setting method, ACL, is specified in Section 8. Four reports that provide limited server-side searching capabilities are described in Section 9. Sections on XML processing (Section 10), Internationalization considerations (Section 11), security considerations (Section 12), and authentication (Section 13) round out the specification. An appendix (Appendix A) provides an XML Document Type Definition (DTD) for the XML elements defined in the specification. 1.1. Terms This document 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. Clemm, et al. Standards Track [Page 6]  RFC 3744 WebDAV Access Control Protocol May 2004 group A 'group' is a principal that represents a set of other principals. privilege A 'privilege' controls access to a particular set of HTTP operations on a resource. aggregate privilege An 'aggregate privilege' is a privilege that contains a set of other privileges. abstract privilege The modifier 'abstract', when applied to a privilege on a resource, means the privilege cannot be set in an access control element (ACE) on that resource. 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 dynamically shared from the ACL of another resource. When a shared ACE changes on the primary resource, it is also changed on inheriting resources. protected property A 'protected property' is one whose value cannot be updated except by a method explicitly defined as updating that specific property. In particular, a protected property cannot be updated with a PROPPATCH request. Clemm, et al. Standards Track [Page 7]  RFC 3744 WebDAV Access Control Protocol May 2004 1.2. Notational Conventions The augmented BNF used by this document to describe protocol elements is described in Section 2.1 of [RFC2616]. Because this augmented BNF uses the basic production rules provided in Section 2.2 of [RFC2616], those rules apply to this document as well. The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in this document are to be interpreted as described in [RFC2119]. Definitions of XML elements in this document use XML element type declarations (as found in XML Document Type Declarations), described in Section 3.2 of [REC-XML]. When an XML element type in the 'DAV:' namespace is referenced in this document outside of the context of an XML fragment, the string 'DAV:' will be prefixed to the element name. 2. Principals A principal is a network resource that represents a distinct human or computational actor that initiates access to network resources. Users and groups are represented as principals in many implementations; other types of principals are also possible. A URI of any scheme MAY be used to identify a principal resource. However, servers implementing this specification MUST expose principal resources at an http(s) URL, which is a privileged scheme that points to resources that have additional properties, as described in Section 4. So, a principal resource can have multiple URIs, 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 be a group, where a group is a principal that represents a set of other principals, called the members of the group. If a person or computational agent matches a principal resource that is a member of a group, they also match the group. Membership in a group is recursive, so if a principal is a member of group GRPA, and GRPA is a member of group GRPB, then the principal is also a member of GRPB. 3. Privileges Ability to perform a given method on a resource MUST 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 MUST be denied any HTTP access to that resource, unless the principal matches an ACE Clemm, et al. Standards Track [Page 8]  RFC 3744 WebDAV Access Control Protocol May 2004 constructed using the DAV:all, DAV:authenticated, or DAV:unauthenticated pseudo-principals (see Section 5.5.1). Servers MUST report a 403 'Forbidden' error if access is denied, except in the case where the privilege restricts the ability to know the resource exists, in which case 404 'Not Found' may be returned. 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 a member of a group. Since these privileges control the ability to update the state of a group, these privileges would be aggregated by the DAV:write privilege on a group, and granting the DAV:write privilege on a group would also grant the add-member and remove-member privileges. Privileges may be declared to be 'abstract' for a given resource, in which case they cannot be set in an ACE on that resource. Aggregate and non-aggregate privileges are both capable of being abstract. Abstract privileges are useful for modeling privileges that otherwise would not be exposed via the protocol. Abstract privileges also provide server implementations with flexibility in implementing the privileges defined in this specification. For example, if a server is incapable of separating the read resource capability from the read ACL capability, it can still model the DAV:read and DAV:read-acl privileges defined in this specification by declaring them abstract, and containing them within a non-abstract aggregate privilege (say, read-all) that holds DAV:read, and DAV:read-acl. In this way, it is possible to set the aggregate privilege, read-all, thus coupling the setting of DAV:read and DAV:read-acl, but it is not possible to set DAV:read, or DAV:read-acl individually. Since aggregate privileges can be abstract, it is also possible to use abstract privileges to group or organize non-abstract privileges. Privilege containment loops are not allowed; therefore, a privilege MUST NOT contain itself. For example, DAV:read cannot contain DAV:read. The set of privileges that apply to a particular resource may vary with the DAV:resourcetype of the resource, as well as between different server implementations. To promote interoperability, however, this specification defines a set of well-known privileges (e.g., DAV:read, DAV:write, DAV:read-acl, DAV:write-acl, DAV:read- current-user-privilege-set, and DAV:all), which can at least be used to classify the other privileges defined on a particular resource. The access permissions on null resources (defined in [RFC2518], Section 3) are solely those they inherit (if any), and they are not discoverable (i.e., the access control properties specified in Clemm, et al. Standards Track [Page 9]  RFC 3744 WebDAV Access Control Protocol May 2004 Section 5 are not defined on null resources). On the transition from null to stateful resource, the initial access control list is set by the server's default ACL value policy (if any). Server implementations MAY define new privileges beyond those defined in this specification. Privileges defined by individual implementations MUST NOT use the DAV: namespace, and instead should use a namespace that they control, such as an http scheme URL. 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. Any implementation-defined privilege that also controls access to GET and PROPFIND must be aggregated under DAV:read - if an ACL grants access to DAV:read, the client may expect that no other privilege needs to be granted to have access to GET and PROPFIND. Additionally, the read privilege MUST control the OPTIONS method. 3.2. DAV:write Privilege The write privilege controls methods that lock a resource or 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. Any implementation-defined privilege that also controls access to methods modifying content, dead properties or collection membership must be aggregated under DAV:write, e.g., if an ACL grants access to DAV:write, the client may expect that no other privilege needs to be granted to have access to PUT and PROPPATCH. 3.3. DAV:write-properties Privilege The DAV:write-properties privilege controls methods that modify the dead properties of the resource, such as PROPPATCH. Whether this privilege may be used to control access to any live properties is determined by the implementation. Any implementation-defined privilege that also controls access to methods modifying dead properties must be aggregated under DAV:write-properties - e.g., if Clemm, et al. Standards Track [Page 10]  RFC 3744 WebDAV Access Control Protocol May 2004 an ACL grants access to DAV:write-properties, the client can safely expect that no other privilege needs to be granted to have access to PROPPATCH. 3.4. DAV:write-content Privilege The DAV:write-content privilege controls methods that modify the content of an existing resource, such as PUT. Any implementation- defined privilege that also controls access to content must be aggregated under DAV:write-content - e.g., if an ACL grants access to DAV:write-content, the client can safely expect that no other privilege needs to be granted to have access to PUT. Note that PUT - when applied to an unmapped URI - creates a new resource and therefore is controlled by the DAV:bind privilege on the parent collection. 3.5. DAV:unlock Privilege The DAV:unlock privilege controls the use of the UNLOCK method by a principal other than the lock owner (the principal that created a lock can always perform an UNLOCK). While the set of users who may lock a resource is most commonly the same set of users who may modify a resource, servers may allow various kinds of administrators to unlock resources locked by others. Any privilege controlling access by non-lock owners to UNLOCK MUST be aggregated under DAV:unlock. A lock owner can always remove a lock by issuing an UNLOCK with the correct lock token and authentication credentials. That is, even if a principal does not have DAV:unlock privilege, they can still remove locks they own. Principals other than the lock owner can remove a lock only if they have DAV:unlock privilege and they issue an UNLOCK with the correct lock token. Lock timeout is not affected by the DAV:unlock privilege. 3.6. DAV:read-acl Privilege The DAV:read-acl privilege controls the use of PROPFIND to retrieve the DAV:acl property of the resource. Clemm, et al. Standards Track [Page 11]  RFC 3744 WebDAV Access Control Protocol May 2004 3.7. DAV:read-current-user-privilege-set Privilege The DAV:read-current-user-privilege-set privilege controls the use of PROPFIND to retrieve the DAV:current-user-privilege-set property of the resource. Clients are intended to use this property to visually indicate in their UI items that are dependent on the permissions of a resource, for example, by graying out resources that are not writable. 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. 3.8. DAV:write-acl Privilege The DAV:write-acl privilege controls use of the ACL method to modify the DAV:acl property of the resource. 3.9. DAV:bind Privilege The DAV:bind privilege allows a method to add a new member URL to the specified collection (for example via PUT or MKCOL). It is ignored for resources that are not collections. 3.10. DAV:unbind Privilege The DAV:unbind privilege allows a method to remove a member URL from the specified collection (for example via DELETE or MOVE). It is ignored for resources that are not collections. Clemm, et al. Standards Track [Page 12]  RFC 3744 WebDAV Access Control Protocol May 2004 3.11. DAV:all Privilege DAV:all is an aggregate privilege that contains the entire set of privileges that can be applied to the resource. 3.12. Aggregation of Predefined Privileges Server implementations are free to aggregate the predefined privileges (defined above in Sections 3.1-3.10) subject to the following limitations: DAV:read-acl MUST NOT contain DAV:read, DAV:write, DAV:write-acl, DAV:write-properties, DAV:write-content, or DAV:read-current-user- privilege-set. DAV:write-acl MUST NOT contain DAV:write, DAV:read, DAV:read-acl, or DAV:read-current-user-privilege-set. DAV:read-current-user-privilege-set MUST NOT contain DAV:write, DAV:read, DAV:read-acl, or DAV:write-acl. DAV:write MUST NOT contain DAV:read, DAV:read-acl, or DAV:read- current-user-privilege-set. DAV:read MUST NOT contain DAV:write, DAV:write-acl, DAV:write- properties, or DAV:write-content. DAV:write MUST contain DAV:bind, DAV:unbind, DAV:write-properties and DAV:write-content. 4. Principal Properties Principals are manifested to clients as a WebDAV resource, identified by a URL. A principal MUST have a non-empty DAV:displayname property (defined in Section 13.2 of [RFC2518]), and a DAV:resourcetype property (defined in Section 13.9 of [RFC2518]). Additionally, a principal MUST report the DAV:principal XML element in the value of the DAV:resourcetype property. The element type declaration for DAV:principal is: Clemm, et al. Standards Track [Page 13]  RFC 3744 WebDAV Access Control Protocol May 2004 This protocol defines the following additional properties for a principal. Since it can be expensive for a server to retrieve access control information, the name and value of these properties SHOULD NOT be returned by a PROPFIND allprop request (as defined in Section 12.14.1 of [RFC2518]). 4.1. DAV:alternate-URI-set This protected property, if non-empty, contains the URIs of network resources with additional descriptive information about the principal. This property identifies additional network resources (i.e., it contains one or more URIs) that may be consulted by a client to gain additional knowledge concerning a principal. One expected use for this property is the storage of an LDAP [RFC2255] scheme URL. A user-agent encountering an LDAP URL could use LDAP [RFC2251] to retrieve additional machine-readable directory information about the principal, and display that information in its user interface. Support for this property is REQUIRED, and the value is empty if no alternate URI exists for the principal. 4.2. DAV:principal-URL A principal may have many URLs, but there must be one 'principal URL' that clients can use to uniquely identify a principal. This protected property contains the URL that MUST be used to identify this principal in an ACL request. Support for this property is REQUIRED. 4.3. DAV:group-member-set This property of a group principal identifies the principals that are direct members of this group. Since a group may be a member of another group, a group may also have indirect members (i.e., the members of its direct members). A URL in the DAV:group-member-set for a principal MUST be the DAV:principal-URL of that principal. 4.4. DAV:group-membership This protected property identifies the groups in which the principal is directly a member. Note that a server may allow a group to be a member of another group, in which case the DAV:group-membership of Clemm, et al. Standards Track [Page 14]  RFC 3744 WebDAV Access Control Protocol May 2004 those other groups would need to be queried in order to determine the groups in which the principal is indirectly a member. Support for this property is REQUIRED. 5. Access Control Properties This specification defines a number of new properties for WebDAV resources. Access control properties may be retrieved just like other WebDAV properties, using the PROPFIND method. Since it is expensive, for many servers, to retrieve access 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. Access control properties (especially DAV:acl and DAV:inherited-acl- set) are defined on the resource identified by the Request-URI of a PROPFIND request. A direct consequence is that if the resource is accessible via multiple URI, the value of access control properties is the same across these URI. HTTP resources that support the WebDAV Access Control Protocol MUST contain the following properties. Null resources (described in Section 3 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. 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. Servers MAY implement DAV:owner as protected property and MAY return an empty DAV:owner element as property value in case no owner information is available. 5.1.1. Example: Retrieving DAV:owner This example shows a client request for the value of the DAV:owner property from a collection resource with URL http://www.example.com/ papers/. The principal making the request is authenticated using Digest authentication. The value of DAV:owner is the URL http:// www.example.com/acl/users/gstein, wrapped in the DAV:href XML element. Clemm, et al. Standards Track [Page 15]  RFC 3744 WebDAV Access Control Protocol May 2004 >> Request << PROPFIND /papers/ HTTP/1.1 Host: www.example.com Content-type: text/xml; charset='utf-8' Content-Length: xxx Depth: 0 Authorization: Digest username='jim', realm='users@example.com', nonce='...', uri='/papers/', response='...', opaque='...' >> Response << HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset='utf-8' Content-Length: xxx http://www.example.com/papers/ http://www.example.com/acl/users/gstein HTTP/1.1 200 OK 5.1.2. Example: An Attempt to Set DAV:owner The following example shows a client request to modify the value of the DAV:owner property on the resource with URL www.example.com/papers>. Since DAV:owner is a protected property on this particular server, it responds with a 207 (Multi-Status) response that contains a 403 (Forbidden) status code for the act of setting DAV:owner. Section 8.2.1 of [RFC2518] describes PROPPATCH status code information, Section 11 of [RFC2518] describes the Clemm, et al. Standards Track [Page 16]  RFC 3744 WebDAV Access Control Protocol May 2004 Multi-Status response and Sections 1.6 and 3.12 of [RFC3253] describe additional error marshaling for PROPPATCH attempts on protected properties. >> Request << PROPPATCH /papers/ HTTP/1.1 Host: www.example.com Content-type: text/xml; charset='utf-8' Content-Length: xxx Depth: 0 Authorization: Digest username='jim', realm='users@example.com', nonce='...', uri='/papers/', response='...', opaque='...' http://www.example.com/acl/users/jim >> Response << HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset='utf-8' Content-Length: xxx http://www.example.com/papers/ HTTP/1.1 403 Forbidden Failure to set protected property (DAV:owner) Clemm, et al. Standards Track [Page 17]  RFC 3744 WebDAV Access Control Protocol May 2004 5.2. DAV:group This property identifies a particular principal as being the 'group' of the resource. This property is commonly found on repositories that implement the Unix privileges model. Servers MAY implement DAV:group as protected property and MAY return an empty DAV:group element as property value in case no group information is available. 5.3. DAV:supported-privilege-set This is a protected property that identifies the privileges defined for the resource. Each privilege appears as an XML element, where aggregate privileges list as sub-elements all of the privileges that they aggregate. (privilege, abstract?, description, supported-privilege*)> An abstract privilege 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. Servers MUST indicate the human language of the description using the xml:lang attribute and SHOULD consider the HTTP Accept-Language request header when selecting one of multiple available languages. It is envisioned that a WebDAV ACL-aware administrative client would list the supported privileges in a dialog box, and allow the user to choose non-abstract privileges to apply in an ACE. The privileges tree is useful programmatically to map well-known privileges (defined by WebDAV or other standards groups) into privileges that are supported by any particular server implementation. The privilege tree also serves to hide complexity in implementations allowing large number of privileges to be defined by displaying aggregates to the user. Clemm, et al. Standards Track [Page 18]  RFC 3744 WebDAV Access Control Protocol May 2004 5.3.1. Example: Retrieving a List of Privileges Supported on a Resource This example shows a client request for the DAV:supported-privilege- set property on the resource http://www.example.com/papers/. The value of the DAV:supported-privilege-set property is a tree of supported privileges (using '[XML Namespace , localname]' to identify each privilege): [DAV:, all] (aggregate, abstract) | +-- [DAV:, read] (aggregate) | +-- [DAV:, read-acl] (abstract) +-- [DAV:, read-current-user-privilege-set] (abstract) | +-- [DAV:, write] (aggregate) | +-- [DAV:, write-acl] (abstract) +-- [DAV:, write-properties] +-- [DAV:, write-content] | +-- [DAV:, unlock] This privilege tree is not normative (except that it reflects the normative aggregation rules given in Section 3.12), and many possible privilege trees are possible. >> Request << PROPFIND /papers/ HTTP/1.1 Host: www.example.com Content-type: text/xml; charset='utf-8' Content-Length: xxx Depth: 0 Authorization: Digest username='gclemm', realm='users@example.com', nonce='...', uri='/papers/', response='...', opaque='...' Clemm, et al. Standards Track [Page 19]  RFC 3744 WebDAV Access Control Protocol May 2004 >> Response << HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset='utf-8' Content-Length: xxx http://www.example.com/papers/ Any operation Read any object Read ACL Read current user privilege set property Write any object Clemm, et al. Standards Track [Page 20]  RFC 3744 WebDAV Access Control Protocol May 2004 Write ACL Write properties Write resource content Unlock resource HTTP/1.1 200 OK 5.4. DAV:current-user-privilege-set DAV:current-user-privilege-set is a protected property containing the exact set of privileges (as computed by the server) granted to the currently authenticated HTTP user. Aggregate privileges and their contained privileges are listed. A user-agent can use the value of this property to adjust its user interface to make actions inaccessible (e.g., by graying out a menu item or button) for which the current principal does not have permission. This property is also useful for determining what operations the current principal can perform, without having to actually execute an operation. Clemm, et al. Standards Track [Page 21]  RFC 3744 WebDAV Access Control Protocol May 2004 If the current user is granted a specific privilege, that privilege must belong to the set of privileges that may be set on this resource. Therefore, each element in the DAV:current-user- privilege-set property MUST identify a non-abstract privilege from the DAV:supported-privilege-set property. 5.4.1. Example: Retrieving the User's Current Set of Assigned Privileges Continuing the example from Section 5.3.1, this example shows a client requesting the DAV:current-user-privilege-set property from the resource with URL http://www.example.com/papers/. The username of the principal making the request is 'khare', and Digest authentication is used in the request. The principal with username 'khare' has been granted the DAV:read privilege. Since the DAV:read privilege contains the DAV:read-acl and DAV:read-current-user- privilege-set privileges (see Section 5.3.1), the principal with username 'khare' can read the ACL property, and the DAV:current- user-privilege-set property. However, the DAV:all, DAV:read-acl, DAV:write-acl and DAV:read-current-user-privilege-set privileges are not listed in the value of DAV:current-user-privilege-set, since (for this example) they are abstract privileges. DAV:write is not listed since the principal with username 'khare' is not listed in an ACE granting that principal write permission. >> Request << PROPFIND /papers/ HTTP/1.1 Host: www.example.com Content-type: text/xml; charset='utf-8' Content-Length: xxx Depth: 0 Authorization: Digest username='khare', realm='users@example.com', nonce='...', uri='/papers/', response='...', opaque='...' Clemm, et al. Standards Track [Page 22]  RFC 3744 WebDAV Access Control Protocol May 2004 >> Response << HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset='utf-8' Content-Length: xxx http://www.example.com/papers/ HTTP/1.1 200 OK 5.5. DAV:acl This is a protected property that specifies the list of access control entries (ACEs), which define what principals are to get what privileges for this resource. Each DAV:ace element specifies the set of privileges to be either granted or denied to a single principal. If the DAV:acl property is empty, no principal is granted any privilege. inherited?)> 5.5.1. ACE Principal The DAV:principal element identifies the principal to which this ACE applies. | property | self)> 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. Clemm, et al. Standards Track [Page 23]  RFC 3744 WebDAV Access Control Protocol May 2004 The current user always matches DAV:all. The current user matches DAV:authenticated only if authenticated. The current user matches DAV:unauthenticated only if not authenticated. DAV:all is the union of DAV:authenticated, and DAV:unauthenticated. For a given request, the user matches either DAV:authenticated, or DAV:unauthenticated, but not both (that is, DAV:authenticated and DAV:unauthenticated are disjoint sets). The current user matches a DAV:property principal in a DAV:acl property of a resource only if the value of the identified property of that resource contains at most one DAV:href XML element, the URI value of DAV:href identifies a principal, and the current user is authenticated as being (or being a member of) that principal. For example, if the DAV:property element contained , the current user would match the DAV:property principal only if the current user is authenticated as matching the principal identified by the DAV:owner property of the resource. The current user matches DAV:self in a DAV:acl property of the resource only if that resource is a principal and that principal matches the current user or, if the principal is a group, a member of that group matches the current user. Some servers may support ACEs applying to those users NOT matching the current principal, e.g., all users not in a particular group. This can be done by wrapping the DAV:principal element with DAV:invert. Clemm, et al. Standards Track [Page 24]  RFC 3744 WebDAV Access Control Protocol May 2004 5.5.2. ACE Grant and Deny Each DAV:grant or DAV:deny element specifies the set of privileges to be either granted or denied to the specified principal. A DAV:grant or DAV:deny element of the DAV:acl of a resource MUST only contain non-abstract elements specified in the DAV:supported-privilege-set of that resource. 5.5.3. ACE Protection A server indicates an ACE is protected by including the DAV:protected element in the ACE. If the ACL of a resource contains an ACE with a DAV:protected element, an attempt to remove that ACE from the ACL MUST fail. 5.5.4. 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. 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. 5.5.5. Example: Retrieving a Resource's Access Control List Continuing the example from Sections 5.3.1 and 5.4.1, this example shows a client requesting the DAV:acl property from the resource with URL http://www.example.com/papers/. There are two ACEs defined in this ACL: Clemm, et al. Standards Track [Page 25]  RFC 3744 WebDAV Access Control Protocol May 2004 ACE #1: The group identified by URL http://www.example.com/acl/ groups/maintainers (the group of site maintainers) is granted DAV:write privilege. Since (for this example) DAV:write contains the DAV:write-acl privilege (see Section 5.3.1), this means the 'maintainers' group can also modify the access control list. ACE #2: All principals (DAV:all) are granted the DAV:read privilege. Since (for this example) DAV:read contains DAV:read-acl and DAV:read-current-user-privilege-set, this means all users (including all members of the 'maintainers' group) can read the DAV:acl property and the DAV:current-user-privilege-set property. >> Request << PROPFIND /papers/ HTTP/1.1 Host: www.example.com Content-type: text/xml; charset='utf-8' Content-Length: xxx Depth: 0 Authorization: Digest username='masinter', realm='users@example.com', nonce='...', uri='/papers/', response='...', opaque='...' >> Response << HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset='utf-8' Content-Length: xxx http://www.example.com/papers/ >http://www.example.com/acl/groups/maintainers Clemm, et al. Standards Track [Page 26]  RFC 3744 WebDAV Access Control Protocol May 2004 HTTP/1.1 200 OK 5.6. DAV:acl-restrictions This protected property defines the types of ACLs supported by this server, to avoid clients needlessly getting errors. When a client tries to set an ACL via the ACL method, the server may reject the attempt to set the ACL as specified. The following properties indicate the restrictions the client must observe before setting an ACL: Deny ACEs are not supported Inverted ACEs are not supported All deny ACEs must occur before any grant ACEs Indicates which principals are required to be present deny-before-grant?, required-principal?)> 5.6.1. DAV:grant-only This element indicates that ACEs with deny clauses are not allowed. Clemm, et al. Standards Track [Page 27]  RFC 3744 WebDAV Access Control Protocol May 2004 5.6.2. DAV:no-invert ACE Constraint This element indicates that ACEs with the element are not allowed. 5.6.3. DAV:deny-before-grant This element indicates that all deny ACEs must precede all grant ACEs. 5.6.4. Required Principals The required principal elements identify which principals must have an ACE defined in the ACL. (all? | authenticated? | unauthenticated? | self? | href* | property*)> For example, the following element requires that the ACL contain a DAV:owner property ACE: 5.6.5. Example: Retrieving DAV:acl-restrictions In this example, the client requests the value of the DAV:acl- restrictions property. Digest authentication provides credentials for the principal operating the client. >> Request << PROPFIND /papers/ HTTP/1.1 Host: www.example.com Content-type: text/xml; charset='utf-8' Content-Length: xxx Depth: 0 Authorization: Digest username='srcarter', realm='users@example.com', nonce='...', uri='/papers/', response='...', opaque='...' Clemm, et al. Standards Track [Page 28]  RFC 3744 WebDAV Access Control Protocol May 2004 >> Response << HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset='utf-8' Content-Length: xxx http://www.example.com/papers/ HTTP/1.1 200 OK 5.7. DAV:inherited-acl-set This protected property contains a set of URLs that identify other resources that also control the access to this resource. To have a privilege on a resource, not only must the ACL on that resource (specified in the DAV:acl property of that resource) grant the privilege, but so must the ACL of each resource identified in the DAV:inherited-acl-set property of that resource. Effectively, the privileges granted by the current ACL are ANDed with the privileges granted by each inherited ACL. Clemm, et al. Standards Track [Page 29]  RFC 3744 WebDAV Access Control Protocol May 2004 5.8. DAV:principal-collection-set This protected property of a resource contains a set of URLs that identify the root collections that contain the principals that are available on the server that implements this resource. A WebDAV Access Control Protocol user agent could use the contents of DAV:principal-collection-set to retrieve the DAV:displayname property (specified in Section 13.2 of [RFC2518]) of all principals on that server, thereby yielding human-readable names for each principal that could be displayed in a user interface. Since different servers can control different parts of the URL namespace, different resources on the same host MAY have different DAV:principal-collection-set values. The collections specified in the DAV:principal-collection-set MAY be located on different hosts from the resource. The URLs in DAV:principal-collection-set SHOULD be http or https scheme URLs. For security and scalability reasons, a server MAY report only a subset of the entire set of known principal collections, and therefore clients should not assume they have retrieved an exhaustive listing. Additionally, a server MAY elect to report none of the principal collections it knows about, in which case the property value would be empty. The value of DAV:principal-collection-set gives the scope of the DAV:principal-property-search REPORT (defined in Section 9.4). Clients use the DAV:principal-property-search REPORT to populate their user interface with a list of principals. Therefore, servers that limit a client's ability to obtain principal information will interfere with the client's ability to manipulate access control lists, due to the difficulty of getting the URL of a principal for use in an ACE. 5.8.1. Example: Retrieving DAV:principal-collection-set In this example, the client requests the value of the DAV:principal- collection-set property on the collection resource identified by URL http://www.example.com/papers/. The property contains the two URLs, http://www.example.com/acl/users/ and http:// www.example.com/acl/groups/, both wrapped in DAV:href XML elements. Digest authentication provides credentials for the principal operating the client. Clemm, et al. Standards Track [Page 30]  RFC 3744 WebDAV Access Control Protocol May 2004 The client might reasonably follow this request with two separate PROPFIND requests to retrieve the DAV:displayname property of the members of the two collections (/acl/users and /acl/groups). This information could be used when displaying a user interface for creating access control entries. >> Request << PROPFIND /papers/ HTTP/1.1 Host: www.example.com Content-type: text/xml; charset='utf-8' Content-Length: xxx Depth: 0 Authorization: Digest username='yarong', realm='users@example.com', nonce='...', uri='/papers/', response='...', opaque='...' >> Response << HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset='utf-8' Content-Length: xxx http://www.example.com/papers/ http://www.example.com/acl/users/ http://www.example.com/acl/groups/ HTTP/1.1 200 OK Clemm, et al. Standards Track [Page 31]  RFC 3744 WebDAV Access Control Protocol May 2004 5.9. 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 << PROPFIND /top/container/ HTTP/1.1 Host: www.example.com Content-type: text/xml; charset='utf-8' Content-Length: xxx Depth: 0 Authorization: Digest username='ejw', realm='users@example.com', nonce='...', uri='/top/container/', response='...', opaque='...' >> Response << HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset='utf-8' Content-Length: xxx xmlns:A='http://www.example.com/acl/'> http://www.example.com/top/container/ http://www.example.com/users/gclemm Clemm, et al. Standards Track [Page 32]  RFC 3744 WebDAV Access Control Protocol May 2004 Any operation Read any object Write any object Create an object Update an object Delete an object Read the ACL Write the ACL Clemm, et al. Standards Track [Page 33]  RFC 3744 WebDAV Access Control Protocol May 2004 http://www.example.com/users/esedlar http://www.example.com/groups/mrktng http://www.example.com/top HTTP/1.1 200 OK Clemm, et al. Standards Track [Page 34]  RFC 3744 WebDAV Access Control Protocol May 2004 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 (using '[XML Namespace , localname]' to identify each privilege): [DAV:, all] (aggregate, abstract) | +-- [DAV:, read] +-- [DAV:, write] (aggregate, abstract) | +-- [http://www.example.com/acl, create] +-- [http://www.example.com/acl, update] +-- [http://www.example.com/acl, delete] +-- [DAV:, read-acl] +-- [DAV:, write-acl] The DAV:current-user-privilege-set property contains two privileges, DAV:read, and DAV:read-acl. This indicates that the current authenticated user only has the ability to read the resource, and read the DAV:acl property on the resource. The DAV:acl property contains a set of four ACEs: ACE #1: The principal identified by the URL http://www.example.com/ users/esedlar is granted the DAV:read, DAV:write, and DAV:read-acl privileges. ACE #2: The principals identified by the URL http://www.example.com/ groups/mrktng are denied the DAV:read privilege. In this example, the principal URL identifies a group. ACE #3: In this ACE, the principal is a property principal, specifically the DAV:owner property. When evaluating this ACE, the value of the DAV:owner property is retrieved, and is examined to see if it contains a DAV:href XML element. If so, the URL within the DAV:href element is read, and identifies a principal. In this ACE, the owner is granted DAV:read-acl, and DAV:write-acl privileges. ACE #4: This ACE grants the DAV:all principal (all users) the DAV:read privilege. This ACE is inherited from the resource http:// www.example.com/top, the parent collection of this resource. Clemm, et al. Standards Track [Page 35]  RFC 3744 WebDAV Access Control Protocol May 2004 6. ACL Evaluation WebDAV ACLs are evaluated in similar manner as ACLs on Windows NT and in NFSv4 [RFC3530]). An ACL is evaluated to determine whether or not access will be granted for a WebDAV request. ACEs are maintained in a particular order, and are evaluated until all of the permissions required by the current request have been granted, at which point the ACL evaluation is terminated and access is granted. If, during ACL evaluation, a ACE (matching the current user) is encountered for a privilege which has not yet been granted, the ACL evaluation is terminated and access is denied. Failure to have all required privileges granted results in access being denied. Note that the semantics of many other existing ACL systems may be represented via this mechanism, by mixing deny and grant ACEs. For example, consider the standard 'rwx' privilege scheme used by UNIX. In this scheme, if the current user is the owner of the file, access is granted if the corresponding privilege bit is set and denied if not set, regardless of the permissions set on the file's group and for the world. An ACL for UNIX permissions of 'r--rw-r--' might be constructed like: Clemm, et al. Standards Track [Page 36]  RFC 3744 WebDAV Access Control Protocol May 2004 and the would be defined as: Note that the client can still get errors from a UNIX server in spite of obeying the , including (adding an ACE specifying a principal other than the ones in the ACL above) or (by trying to reorder the ACEs in the example above), as these particular implementation semantics are too complex to be captured with the simple (but general) declarative restrictions. 7. Access Control and existing methods This section defines the impact of access control functionality on existing methods. 7.1. Any HTTP method 7.1.1. Error Handling The WebDAV ACL mechanism requires the usage of HTTP method 'preconditions' as described in section 1.6 of RFC3253 for ALL HTTP methods. All HTTP methods have an additional precondition called DAV:need-privileges. If an HTTP method fails due to insufficient privileges, the response body to the '403 Forbidden' error MUST contain the element, which in turn contains the Clemm, et al. Standards Track [Page 37]  RFC 3744 WebDAV Access Control Protocol May 2004 element, which contains one or more elements indicating which resource had insufficient privileges, and what the lacking privileges were: Since some methods require multiple permissions on multiple resources, this information is needed to resolve any ambiguity. There is no requirement that all privilege violations be reported - for implementation reasons, some servers may only report the first privilege violation. For example: >> Request << MOVE /a/b/ HTTP/1.1 Host: www.example.com Destination: http://www.example.com/c/d >> Response << HTTP/1.1 403 Forbidden Content-Type: text/xml; charset='utf-8' Content-Length: xxx /a /c 7.2. 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. A value of 'access-control' in the DAV header MUST indicate that the server supports all MUST level requirements and REQUIRED features specified in this document. Clemm, et al. Standards Track [Page 38]  RFC 3744 WebDAV Access Control Protocol May 2004 7.2.1. Example - OPTIONS >> Request << OPTIONS /foo.html HTTP/1.1 Host: www.example.com Content-Length: 0 >> Response << HTTP/1.1 200 OK DAV: 1, 2, access-control Allow: OPTIONS, GET, PUT, PROPFIND, PROPPATCH, ACL In this example, the OPTIONS response indicates that the server supports access control and that /foo.html can have its access control list modified by the ACL method. 7.3. MOVE When a resource is moved from one location to another due to a MOVE request, the non-inherited and non-protected ACEs in the DAV:acl property of the resource MUST NOT be modified, or the MOVE request fails. Handling of inherited and protected ACEs is intentionally undefined to give server implementations flexibility in how they implement ACE inheritance and protection. 7.4. COPY The DAV:acl property on the resource at the destination of a COPY MUST be the same as if the resource was created by an individual resource creation request (e.g., MKCOL, PUT). Clients wishing to preserve the DAV:acl property across a copy need to read the DAV:acl property prior to the COPY, then perform an ACL operation on the new resource at the destination to restore, insofar as this is possible, the original access control list. 7.5. LOCK A lock on a resource ensures that only the lock owner can modify ACEs that are not inherited and not protected (these are the only ACEs that a client can modify with an ACL request). A lock does not protect inherited or protected ACEs, since a client cannot modify them with an ACL request on that resource. Clemm, et al. Standards Track [Page 39]  RFC 3744 WebDAV Access Control Protocol May 2004 8. Access Control Methods 8.1. ACL The ACL method modifies the access control list (which can be read via the DAV:acl property) of a resource. Specifically, the ACL method only permits modification to ACEs that are not inherited, and are not protected. An ACL method invocation modifies all non- inherited and non-protected ACEs in a resource's access control list to exactly match the ACEs contained within in the DAV:acl XML element (specified in Section 5.5) of the request body. An ACL request body MUST contain only one DAV:acl XML element. Unless the non-inherited and non-protected ACEs of the DAV:acl property of the resource can be updated to be exactly the value specified in the ACL request, the ACL request MUST fail. It is possible that the ACEs visible to the current user in the DAV:acl property may only be a portion of the complete set of ACEs on that resource. If this is the case, an ACL request only modifies the set of ACEs visible to the current user, and does not affect any non-visible ACE. In order to avoid overwriting DAV:acl changes by another client, a client SHOULD acquire a WebDAV lock on the resource before retrieving the DAV:acl property of a resource that it intends on updating. Implementation Note: Two common operations are to add or remove an ACE from an existing access control list. To accomplish this, a client uses the PROPFIND method to retrieve the value of the DAV:acl property, then parses the returned access control list to remove all inherited and protected ACEs (these ACEs are tagged with the DAV:inherited and DAV:protected XML elements). In the remaining set of non-inherited, non-protected ACEs, the client can add or remove one or more ACEs before submitting the final ACE set in the request body of the ACL method. 8.1.1. ACL Preconditions An implementation MUST enforce the following constraints on an ACL request. If the constraint is violated, a 403 (Forbidden) or 409 (Conflict) response MUST be returned and the indicated XML element MUST be returned as a child of a top level DAV:error element in an XML response body. Though these status elements are generally expressed as empty XML elements (and are defined as EMPTY in the DTD), implementations MAY return additional descriptive XML elements as children of the status Clemm, et al. Standards Track [Page 40]  RFC 3744 WebDAV Access Control Protocol May 2004 element. Clients MUST be able to accept children of these status elements. Clients that do not understand the additional XML elements should ignore them. (DAV:no-ace-conflict): The ACEs submitted in the ACL request MUST NOT conflict with each other. This is a catchall error code indicating that an implementation-specific ACL restriction has been violated. (DAV:no-protected-ace-conflict): The ACEs submitted in the ACL request MUST NOT conflict with the protected ACEs on the resource. For example, if the resource has a protected ACE granting DAV:write to a given principal, then it would not be consistent if the ACL request submitted an ACE denying DAV:write to the same principal. (DAV:no-inherited-ace-conflict): The ACEs submitted in the ACL request MUST NOT conflict with the inherited ACEs on the resource. For example, if the resource inherits an ACE from its parent collection granting DAV:write to a given principal, then it would not be consistent if the ACL request submitted an ACE denying DAV:write to the same principal. Note that reporting of this error will be implementation-dependent. Implementations MUST either report this error or allow the ACE to be set, and then let normal ACE evaluation rules determine whether the new ACE has any impact on the privileges available to a specific principal. (DAV:limited-number-of-aces): The number of ACEs submitted in the ACL request MUST NOT exceed the number of ACEs allowed on that resource. However, ACL-compliant servers MUST support at least one ACE granting privileges to a single principal, and one ACE granting privileges to a group. (DAV:deny-before-grant): All non-inherited deny ACEs MUST precede all non-inherited grant ACEs. (DAV:grant-only): The ACEs submitted in the ACL request MUST NOT include a deny ACE. This precondition applies only when the ACL restrictions of the resource include the DAV:grant-only constraint (defined in Section 5.6.1). (DAV:no-invert): The ACL request MUST NOT include a DAV:invert element. This precondition applies only when the ACL semantics of the resource includes the DAV:no-invert constraint (defined in Section 5.6.2). (DAV:no-abstract): The ACL request MUST NOT attempt to grant or deny an abstract privilege (see Section 5.3). Clemm, et al. Standards Track [Page 41]  RFC 3744 WebDAV Access Control Protocol May 2004 (DAV:not-supported-privilege): The ACEs submitted in the ACL request MUST be supported by the resource. (DAV:missing-required-principal): The result of the ACL request MUST have at least one ACE for each principal identified in a DAV:required-principal XML element in the ACL semantics of that resource (see Section 5.5). (DAV:recognized-principal): Every principal URL in the ACL request MUST identify a principal resource. (DAV:allowed-principal): The principals specified in the ACEs submitted in the ACL request MUST be allowed as principals for the resource. For example, a server where only authenticated principals can access resources would not allow the DAV:all or DAV:unauthenticated principals to be used in an ACE, since these would allow unauthenticated access to resources. 8.1.2. Example: the ACL method In the following example, user 'fielding', authenticated by information in the Authorization header, grants the principal identified by the URL http://www.example.com/users/esedlar (i.e., the user 'esedlar') read and write privileges, grants the owner of the resource read-acl and write-acl privileges, and grants everyone read privileges. >> Request << ACL /top/container/ HTTP/1.1 Host: www.example.com Content-Type: text/xml; charset='utf-8' Content-Length: xxxx Authorization: Digest username='fielding', realm='users@example.com', nonce='...', uri='/top/container/', response='...', opaque='...' http://www.example.com/users/esedlar Clemm, et al. Standards Track [Page 42]  RFC 3744 WebDAV Access Control Protocol May 2004 >> Response << HTTP/1.1 200 OK 8.1.3. Example: ACL method failure due to protected ACE conflict In the following request, user 'fielding', authenticated by information in the Authorization header, attempts to deny the principal identified by the URL http://www.example.com/users/esedlar (i.e., the user 'esedlar') write privileges. Prior to the request, the DAV:acl property on the resource contained a protected ACE (see Section 5.5.3) granting DAV:owner the DAV:read and DAV:write privileges. The principal identified by URL http://www.example.com/ users/esedlar is the owner of the resource. The ACL method invocation fails because the submitted ACE conflicts with the protected ACE, thus violating the semantics of ACE protection. >> Request << ACL /top/container/ HTTP/1.1 Host: www.example.com Content-Type: text/xml; charset='utf-8' Content-Length: xxxx Authorization: Digest username='fielding', realm='users@example.com', nonce='...', uri='/top/container/', response='...', opaque='...' Clemm, et al. Standards Track [Page 43]  RFC 3744 WebDAV Access Control Protocol May 2004 http://www.example.com/users/esedlar >> Response << HTTP/1.1 403 Forbidden Content-Type: text/xml; charset='utf-8' Content-Length: xxx 8.1.4. Example: ACL method failure due to an inherited ACE conflict In the following request, user 'ejw', authenticated by information in the Authorization header, tries to change the access control list on the resource http://www.example.com/top/index.html. This resource has two inherited ACEs. Inherited ACE #1 grants the principal identified by URL http:// www.example.com/users/ejw (i.e., the user 'ejw') http:// www.example.com/privs/write-all and DAV:read-acl privileges. On this server, http://www.example.com/privs/write-all is an aggregate privilege containing DAV:write, and DAV:write-acl. Inherited ACE #2 grants principal DAV:all the DAV:read privilege. The request attempts to set a (non-inherited) ACE, denying the principal identified by the URL http://www.example.com/users/ejw (i.e., the user 'ejw') DAV:write permission. This conflicts with inherited ACE #1. Note that the decision to report an inherited ACE conflict is specific to this server implementation. Another server implementation could have allowed the new ACE to be set, and then used normal ACE evaluation rules to determine whether the new ACE has any impact on the privileges available to a principal. Clemm, et al. Standards Track [Page 44]  RFC 3744 WebDAV Access Control Protocol May 2004 >> Request << ACL /top/index.html HTTP/1.1 Host: www.example.com Content-Type: text/xml; charset='utf-8' Content-Length: xxxx Authorization: Digest username='ejw', realm='users@example.com', nonce='...', uri='/top/index.html', response='...', opaque='...' http://www.example.com/users/ejw >> Response << HTTP/1.1 403 Forbidden Content-Type: text/xml; charset='utf-8' Content-Length: xxx 8.1.5. Example: ACL method failure due to an attempt to set grant and deny in a single ACE In this example, user 'ygoland', authenticated by information in the Authorization header, tries to change the access control list on the resource http://www.example.com/diamond/engagement-ring.gif. The ACL request includes a single, syntactically and semantically incorrect ACE, which attempts to grant the group identified by the URL http:// www.example.com/users/friends DAV:read privilege and deny the principal identified by URL http://www.example.com/users/ygoland-so (i.e., the user 'ygoland-so') DAV:read privilege. However, it is illegal to have multiple principal elements, as well as both a grant and deny element in the same ACE, so the request fails due to poor syntax. Clemm, et al. Standards Track [Page 45]  RFC 3744 WebDAV Access Control Protocol May 2004 >> Request << ACL /diamond/engagement-ring.gif HTTP/1.1 Host: www.example.com Content-Type: text/xml; charset='utf-8' Content-Length: xxxx Authorization: Digest username='ygoland', realm='users@example.com', nonce='...', uri='/diamond/engagement-ring.gif', response='...', opaque='...' http://www.example.com/users/friends http://www.example.com/users/ygoland-so >> Response << HTTP/1.1 400 Bad Request Content-Length: 0 Note that if the request had been divided into two ACEs, one to grant, and one to deny, the request would have been syntactically well formed. 9. Access Control Reports 9.1. REPORT Method The REPORT method (defined in Section 3.6 of [RFC3253]) provides an extensible mechanism for obtaining information about a resource. Unlike the PROPFIND method, which returns the value of one or more named properties, the REPORT method can involve more complex processing. REPORT is valuable in cases where the server has access to all of the information needed to perform the complex request (such as a query), and where it would require multiple requests for the client to retrieve the information needed to perform the same request. Clemm, et al. Standards Track [Page 46]  RFC 3744 WebDAV Access Control Protocol May 2004 A server that supports the WebDAV Access Control Protocol MUST support the DAV:expand-property report (defined in Section 3.8 of [RFC3253]). 9.2. DAV:acl-principal-prop-set Report The DAV:acl-principal-prop-set report returns, for all principals in the DAV:acl property (of the Request-URI) that are identified by http(s) URLs or by a DAV:property principal, the value of the properties specified in the REPORT request body. In the case where a principal URL appears multiple times, the DAV:acl-principal-prop-set report MUST return the properties for that principal only once. Support for this report is REQUIRED. One expected use of this report is to retrieve the human readable name (found in the DAV:displayname property) of each principal found in an ACL. This is useful for constructing user interfaces that show each ACE in a human readable form. Marshalling The request body MUST be a DAV:acl-principal-prop-set XML element. ANY value: a sequence of one or more elements, with at most one DAV:prop element. prop: see RFC 2518, Section 12.11 This report is only defined when the Depth header has value '0'; other values result in a 400 (Bad Request) error response. Note that [RFC3253], Section 3.6, states that if the Depth header is not present, it defaults to a value of '0'. The response body for a successful request MUST be a DAV:multistatus XML element (i.e., the response uses the same format as the response for PROPFIND). In the case where there are no response elements, the returned multistatus XML element is empty. multistatus: see RFC 2518, Section 12.9 The response body for a successful DAV:acl-principal-prop-set REPORT request MUST contain a DAV:response element for each principal identified by an http(s) URL listed in a DAV:principal XML element of an ACE within the DAV:acl property of the resource identified by the Request-URI. Clemm, et al. Standards Track [Page 47]  RFC 3744 WebDAV Access Control Protocol May 2004 Postconditions: (DAV:number-of-matches-within-limits): The number of matching principals must fall within server-specific, predefined limits. For example, this condition might be triggered if a search specification would cause the return of an extremely large number of responses. 9.2.1. Example: DAV:acl-principal-prop-set Report Resource http://www.example.com/index.html has an ACL with three ACEs: ACE #1: All principals (DAV:all) have DAV:read and DAV:read-current- user-privilege-set access. ACE #2: The principal identified by http://www.example.com/people/ gstein (the user 'gstein') is granted DAV:write, DAV:write-acl, DAV:read-acl privileges. ACE #3: The group identified by http://www.example.com/groups/authors (the 'authors' group) is granted DAV:write and DAV:read-acl privileges. The following example shows a DAV:acl-principal-prop-set report requesting the DAV:displayname property. It returns the value of DAV:displayname for resources http://www.example.com/people/gstein and http://www.example.com/groups/authors , but not for DAV:all, since this is not an http(s) URL. >> Request << REPORT /index.html HTTP/1.1 Host: www.example.com Content-Type: text/xml; charset='utf-8' Content-Length: xxxx Depth: 0 Clemm, et al. Standards Track [Page 48]  RFC 3744 WebDAV Access Control Protocol May 2004 >> Response << HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset='utf-8' Content-Length: xxxx http://www.example.com/people/gstein Greg Stein HTTP/1.1 200 OK http://www.example.com/groups/authors Site authors HTTP/1.1 200 OK 9.3. DAV:principal-match REPORT The DAV:principal-match REPORT is used to identify all members (at any depth) of the collection identified by the Request-URI that are principals and that match the current user. In particular, if the collection contains principals, the report can be used to identify all members of the collection that match the current user. Alternatively, if the collection contains resources that have a property that identifies a principal (e.g., DAV:owner), the report can be used to identify all members of the collection whose property identifies a principal that matches the current user. For example, this report can return all of the resources in a collection hierarchy that are owned by the current user. Support for this report is REQUIRED. Marshalling: The request body MUST be a DAV:principal-match XML element. Clemm, et al. Standards Track [Page 49]  RFC 3744 WebDAV Access Control Protocol May 2004 ANY value: an element whose value identifies a property. The expectation is the value of the named property typically contains an href element that contains the URI of a principal prop: see RFC 2518, Section 12.11 This report is only defined when the Depth header has value '0'; other values result in a 400 (Bad Request) error response. Note that [RFC3253], Section 3.6, states that if the Depth header is not present, it defaults to a value of '0'. The response body for a successful request MUST be a DAV:multistatus XML element. In the case where there are no response elements, the returned multistatus XML element is empty. multistatus: see RFC 2518, Section 12.9 The response body for a successful DAV:principal-match REPORT request MUST contain a DAV:response element for each member of the collection that matches the current user. When the DAV:principal-property element is used, a match occurs if the current user is matched by the principal identified by the URI found in the DAV:href element of the property identified by the DAV:principal-property element. When the DAV:self element is used in a DAV:principal-match report issued against a group, it matches the group if a member identifies the same principal as the current user. If DAV:prop is specified in the request body, the properties specified in the DAV:prop element MUST be reported in the DAV:response elements. 9.3.1. Example: DAV:principal-match REPORT The following example identifies the members of the collection identified by the URL http://www.example.com/doc that are owned by the current user. The current user ('gclemm') is authenticated using Digest authentication. >> Request << REPORT /doc/ HTTP/1.1 Host: www.example.com Authorization: Digest username='gclemm', realm='users@example.com', nonce='...', uri='/papers/', response='...', opaque='...' Content-Type: text/xml; charset='utf-8' Content-Length: xxxx Depth: 0 Clemm, et al. Standards Track [Page 50]  RFC 3744 WebDAV Access Control Protocol May 2004 >> Response << HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset='utf-8' Content-Length: xxxx http://www.example.com/doc/foo.html HTTP/1.1 200 OK http://www.example.com/doc/img/bar.gif HTTP/1.1 200 OK 9.4. DAV:principal-property-search REPORT The DAV:principal-property-search REPORT performs a search for all principals whose properties contain character data that matches the search criteria specified in the request. One expected use of this report is to discover the URL of a principal associated with a given person or group by searching for them by name. This is done by searching over DAV:displayname, which is defined on all principals. The actual search method (exact matching vs. substring matching vs, prefix-matching, case-sensitivity) deliberately is left to the server implementation to allow implementation on a wide set of possible user management systems. In cases where the implementation of DAV:principal-property-search is not constrained by the semantics of an underlying user management repository, preferred default semantics are caseless substring matches. For implementation efficiency, servers do not typically support searching on all properties. A search requesting properties that are not searchable for a particular principal will not match that principal. Support for the DAV:principal-property-search report is REQUIRED. Clemm, et al. Standards Track [Page 51]  RFC 3744 WebDAV Access Control Protocol May 2004 Implementation Note: The value of a WebDAV property is a sequence of well-formed XML, and hence can include any character in the Unicode/ISO-10646 standard, that is, most known characters in human languages. Due to the idiosyncrasies of case mapping across human languages, implementation of case-insensitive matching is non-trivial. Implementors of servers that do perform substring matching are strongly encouraged to consult 'The Unicode Standard' [UNICODE4], especially Section 5.18, Subsection 'Caseless Matching', for guidance when implementing their case-insensitive matching algorithms. Implementation Note: Some implementations of this protocol will use an LDAP repository for storage of principal metadata. The schema describing each attribute (akin to a WebDAV property) in an LDAP repository specifies whether it supports case-sensitive or caseless searching. One of the benefits of leaving the search method to the discretion of the server implementation is the default LDAP attribute search behavior can be used when implementing the DAV:principal-property-search report. Marshalling: The request body MUST be a DAV:principal-property-search XML element containing a search specification and an optional list of properties. For every principal that matches the search specification, the response will contain the value of the requested properties on that principal. ((property-search+), prop?, apply-to-principal-collection-set?) > By default, the report searches all members (at any depth) of the collection identified by the Request-URI. If DAV:apply-to- principal-collection-set is specified in the request body, the request is applied instead to each collection identified by the DAV:principal-collection-set property of the resource identified by the Request-URI. The DAV:property-search element contains a prop element enumerating the properties to be searched and a match element, containing the search string. prop: see RFC 2518, Section 12.11 Clemm, et al. Standards Track [Page 52]  RFC 3744 WebDAV Access Control Protocol May 2004 Multiple property-search elements or multiple elements within a DAV:prop element will be interpreted with a logical AND. This report is only defined when the Depth header has value '0'; other values result in a 400 (Bad Request) error response. Note that [RFC3253], Section 3.6, states that if the Depth header is not present, it defaults to a value of '0'. The response body for a successful request MUST be a DAV:multistatus XML element. In the case where there are no response elements, the returned multistatus XML element is empty. multistatus: see RFC 2518, Section 12.9 The response body for a successful DAV:principal-property-search REPORT request MUST contain a DAV:response element for each principal whose property values satisfy the search specification given in DAV:principal-property-search. If DAV:prop is specified in the request body, the properties specified in the DAV:prop element MUST be reported in the DAV:response elements. Preconditions: None Postconditions: (DAV:number-of-matches-within-limits): The number of matching principals must fall within server-specific, predefined limits. For example, this condition might be triggered if a search specification would cause the return of an extremely large number of responses. 9.4.1. Matching There are several cases to consider when matching strings. The easiest case is when a property value is 'simple' and has only character information item content (see [REC-XML-INFOSET]). For example, the search string 'julian' would match the DAV:displayname property with value 'Julian Reschke'. Note that the on-the-wire marshaling of DAV:displayname in this case is: Julian Reschke Clemm, et al. Standards Track [Page 53]  RFC 3744 WebDAV Access Control Protocol May 2004 The name of the property is encoded into the XML element information item, and the character information item content of the property is 'Julian Reschke'. A more complicated case occurs when properties have mixed content (that is, compound values consisting of multiple child element items, other types of information items, and character information item content). Consider the property 'aprop' in the namespace 'http:// www.example.com/props/', marshaled as: {cdata 0}{cdata 1} {cdata 2}{cdata 3} In this case, matching is performed on each individual contiguous sequence of character information items. In the example above, a search string would be compared to the four following strings: {cdata 0} {cdata 1} {cdata 2} {cdata 3} That is, four individual matches would be performed, one each for {cdata 0}, {cdata 1}, {cdata 2}, and {cdata 3}. 9.4.2. Example: successful DAV:principal-property-search REPORT In this example, the client requests the principal URLs of all users whose DAV:displayname property contains the substring 'doE' and whose 'title' property in the namespace 'http://BigCorp.com/ns/' (that is, their professional title) contains 'Sales'. In addition, the client requests five properties to be returned with the matching principals: In the DAV: namespace: displayname In the http://www.example.com/ns/ namespace: department, phone, office, salary Clemm, et al. Standards Track [Page 54]  RFC 3744 WebDAV Access Control Protocol May 2004 The response shows that two principal resources meet the search specification, 'John Doe' and 'Zygdoebert Smith'. The property 'salary' in namespace 'http://www.example.com/ns/' is not returned, since the principal making the request does not have sufficient access permissions to read this property. >> Request << REPORT /users/ HTTP/1.1 Host: www.example.com Content-Type: text/xml; charset=utf-8 Content-Length: xxxx Depth: 0 doE Sales >> Response << HTTP/1.1 207 Multi-Status Content-Type: text/xml; charset=utf-8 Content-Length: xxxx http://www.example.com/users/jdoe Clemm, et al. Standards Track [Page 55]  RFC 3744 WebDAV Access Control Protocol May 2004 John Doe Widget Sales 234-4567 209 HTTP/1.1 200 OK