INTERNET-DRAFT Geoffrey Clemm, Rational Software draft-ietf-webdav-acl-02 Anne Hopkins, Microsoft Corporation Eric Sedlar, Oracle Corporation Expires January 14, 2001 July 14, 2000 Access Control Extensions to WebDAV Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document specifies a set of methods, headers, and resource-types that define the WebDAV Access Control extensions to the HTTP/1.1 protocol. Sedlar, Clemm, Hopkins [Page 1] INTERNET-DRAFT WebDAV ACL July 14, 2000 Table of Contents 1 INTRODUCTION............................................3 1.1 Notational Conventions................................3 2 PRINCIPALS..............................................3 3 RIGHTS..................................................4 3.1 DAV:access-rights property............................5 3.2 Rights defined by WebDAV..............................6 3.2.1 read Right........................................6 3.2.2 write Right.......................................7 3.2.3 readacl Right.....................................7 3.2.4 writeacl Right....................................7 3.2.5 all Right.........................................7 4 ACCESS CONTROL PROPERTIES...............................7 4.1 Retrieving Access Control Information................11 4.1.1 Example: Retrieving Access Control information...11 4.2 Setting Access Control Information...................12 4.2.1 Example: Setting Access Control information......13 5 USING ACLS.............................................14 5.1 System Controlled Rights.............................14 5.2 Special Principal Identifiers........................15 5.3 ACL Semantics Options................................15 5.3.1 FirstSpecific....................................16 5.3.2 ExplicitDenyPrecedence...........................16 6 ACL INHERITANCE........................................18 6.1 Inheritable ACEs.....................................18 6.2 Propagate ACE but do not use for Access Check on this resource....19 6.3 Propagate to immediate children only.................19 6.4 Protect ACL from inheritance.........................19 7 XML SCHEMA FOR DEFINED ELEMENTS........................20 8 INTERNATIONALIZATION CONSIDERATIONS....................21 9 SECURITY CONSIDERATIONS................................21 10 SCALABILITY..........................................21 11 AUTHENTICATION.......................................21 12 IANA CONSIDERATIONS..................................21 13 INTELLECTUAL PROPERTY................................21 14 ACKNOWLEDGEMENTS.....................................22 15 INDEX................................................22 Clemm,Hopkins,Sedlar [Page 2] INTERNET-DRAFT WebDAV ACL July 14, 2000 16 REFERENCES...........................................22 17 AUTHORS' ADDRESSES...................................23 18 STILL TO DO :........................................23 19 OPEN ISSUES:.........................................25 1 INTRODUCTION The underlying principle of access control is that who you are determines how you can access a resource. The "who you are" is defined by a "principal" identifier; users, client software, servers, and groups of the previous have principal identifiers. The "how" is determined by an "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 rights that are either granted or denied to that principal. 1.1 Notational Conventions The augmented BNF used by this document to describe protocol elements is described in Section 2.1 of [RFC2068]. Because this augmented BNF uses the basic production rules provided in Section 2.2 of [RFC2068], 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]. 2 PRINCIPALS A principal identifies an entity that can be given access rights to HTTP resources. On many implementations, a user or a group will be examples of principals, but other types of principals are possible. For the most part, any classification or other information about the entity identified by a principal is opaque with respect to this specification, and is dependent on the implementation. Principals are manifested to clients as a HTTP resource, identified by a URL. The set of properties exposed by that resource are implementation dependent, although certain properties are required by this specification. Those properties include: . DAV:principalname: A 'live' property containing the name used to authenticate this principal (typically typed into a login prompt/dialog). [OPTIONAL] Clemm,Hopkins,Sedlar [Page 3] INTERNET-DRAFT WebDAV ACL July 14, 2000 . DAV:displayname: A property containing a human-readable description of this principal. This property may be "live" and not settable via PROPPATCH. [REQUIRED] . DAV:principal-type: A 'live' property containing a classification word for this principal. The values DAV:user and DAV:group are choices for value of this property recommended by this spec. The presence of this property can be used to distinguish it as a principal from other resources on a WebDAV server. (Note that DAV:resourcetype may not be used, as all collections must use the value "collection" for DAV:resourcetype, which wouldn't distinguish normal collections from principal collections.) [REQUIRED] Server implementations may include any other descriptive information for a principal via properties. A principal resource may or may not be a collection. A collection principal may only contain other principals (not other types of resources). Servers that support aggregation of principals (e.g. groups of users or other groups) MUST manifest them as collection principals. The WebDAV methods for examining maintaining collections (e.g. DELETE, PROPFIND) may be used to maintain collection principals. Membership in a collection principal is recursive, so a principal in a collection principal A contained by collection principal B is a member of both collection principals. Implementations not supporting recursive membership in principal collections can return an error if the client attempts to bind collection principals into other collection principals. Using WebDAV methods to alter the content of a principal (e.g. using PROPPATCH or PUT) is outside the scope of this specification, and is not required, recommended, or forbidden by this spec. 3 RIGHTS A right controls access to a particular set of HTTP operations on a resource. The set of rights that apply to a particular resource may vary with the DAV:resourcetype of the resource, as well as between different server implementations. To promote interoperability, however, WebDAV defines a set of well-known rights (e.g. DAV:read and DAV:write), which can at least be used to set some context to the other rights defined on a particular resource. Rights may be aggregates of other rights. For example, one implementation may split out a right controlling the ability to add children to a collection from the right allowing a resource to be removed from a collection. Since these rights control the ability to write to a collection, these rights would be aggregated by the DAV:write right. The relationships between atomic rights and aggregate rights can be discovered via the DAV:access-rights property on a particular resource. Servers may specify some rights as abstract, which means that it MUST not Clemm,Hopkins,Sedlar [Page 4] INTERNET-DRAFT WebDAV ACL July 14, 2000 appear in an ACL, but is described in the DAV:access-rights property to aid in setting context. Server implementations must return the same response to the DAV:access-rights property on all of the resources with the same DAV:resourcetype value. 3.1 DAV:access-rights property The DAV:access-rights property is a live property that contains the rights aggregation tree. The DAV:access-rights property MUST be available on every resource available via a WebDAV Access Control-compliant server. Each right appears as an XML element, where aggregate rights list all of their children as sub- elements. Each right element can contain the following attributes: . abstract (Boolean): 'true' if this right MUST NOT be used in an ACL/ACE. Defaults to 'false.' Note: an abstract right need not be an aggregate right. . Description (string): a human-readable description of what this right controls access to. [REQUIRED]. The server MAY localize this description, based on the Accept-Language header of the request. For example, the following response might be generated to a request on a WebDAV server. Request PROPFIND /file HTTP/1.1 Host: www.foo.bar Content-type: text/xml; charset="utf-8" Accept-Language: en-us Depth: 0 Content-Length: xxx Response HTTP/1.1 207 Multi-Status Content-Type: text/xml Content-Length: xxx http://www.foo.bar/file HTTP/1.1 200 OK Clemm,Hopkins,Sedlar [Page 5] INTERNET-DRAFT WebDAV ACL July 14, 2000 It is envisioned that a WebDAV ACL-aware administrative client would list the available rights in a dialog box, and allow the user to choose non-abstract rights to apply in an ACE. The rights tree is useful programmatically to map well-known rights (defined by WebDAV or other standards groups) into rights that are supported by any particular server implementation. 3.2 Rights defined by WebDAV The rights defined by WebDAV access control MUST be present in the DAV:access-rights property, although they may be abstract (and not usable within an ACE on a particular implementation). Ability to perform a given method on a resource MUST be controlled by some right. Authors of Internet drafts that define new methods must specify which right (by defining a new right, or mapping to one below) is required to perform the method. A principal with no rights to a resource should be denied any HTTP access to that resource. 3.2.1read Right Name: DAV:read Purpose: The read right provides and restricts access to information regarding the state of the resource, including the resource's properties. Affected methods include GET and PROPFIND. The read right does not affect the OPTIONS method since it reflects capabilities rather than state. Clemm,Hopkins,Sedlar [Page 6] INTERNET-DRAFT WebDAV ACL July 14, 2000 3.2.2write Right Name: DAV:write Purpose: The write right affects the same methods as the Write Lock. Please refer to [WEBDAV] section 5.3 for the list of affected methods. Note however, that a write lock is a different mechanism than a write access change, although they affect the same methods, they have independent methods to set them and independent error codes. 3.2.3readacl Right Name: DAV:readacl Purpose: The readacl right provides and restricts access to the DAV:acl property of this resource, rather than the DAV:read right. If a user has the readacl right and not the read right, the DAV:acl and DAV:access-rights properties MUST be accessible via PROPFIND, and the GET method is not authorized. If a user has the read right and not the readacl right, the DAV:acl and DAV:access-rights properties will not be included in any PROPFIND requests on the associated resource. 3.2.4writeacl Right Name: DAV:writeacl Purpose: The writeacl right provides and restricts access to the DAV:acl and DAV:owner properties. 3.2.5all Right Name: DAV:all Purpose: The DAV:all right controls all other rights on this resource. If the DAV:all right appears in an ACE, it is an error to have any other right in that ACE. This right is merely shorthand for all of the rights enumerated in the access-rights property, and should not control access to rights not exposed via that route. 4 ACCESS CONTROL PROPERTIES This specification defines a number of new properties for WebDAV resources. Access control properties may be set and retrieved just like other WebDAV properties, using the PROPFIND and PROPPATCH method (subject to permissions and 'liveness.' An HTTP resource on a WebDAV Access Control-compliant server MUST contain the following properties: . DAV:owner: A property containing the principal information identifying a particular user as the owner of the resource. Clemm,Hopkins,Sedlar [Page 7] INTERNET-DRAFT WebDAV ACL July 14, 2000 This property is readable by anyone with read access to the resource. [REQUIRED] . DAV:rights: A 'live' readonly property containing the list of rights of the currently authenticated HTTP user. The read right controls read access to this property. [REQUIRED] . DAV:acl: A 'live' property containing one or more DAV:ace tags, which specify which principals are to get access to what rights, for the resource with this ACL property. [REQUIRED] . DAV:aclsemantics: A readonly property indicating the ACL semantics model supported by the system. [REQUIRED] . DAV:protectaclfrominheritance: A "live" property indicating that the ACL does not inherit any ACEs. If this property is present, the ACL should contain no ACEs with the DAV:inherited element present. If this property is not present and the system supports ACL inheritance, then the ACL will contain inheritable ACEs from its parent resource. If a resource without this property present is updated with this property, it is a client choice whether to remove the inherited ACEs or retain them but remove the DAV:inherited element from the ACEs. [OPTIONAL] The DAV:owner element contains one or more of the following XML elements: . DAV:href: This contains the URI to the principal resource that is the 'owner' of the resource. Normally, an attempt to PROPPATCH this property will result in a 401 (Not Authorized) error. The principal indicated by the owner property is implicitly granted readacl and writeacl rights. This enables the owner to restore an appropriate ACL in the case that it becomes maliciously or accidently corrupted such that no principal is granted the writeacl right by any ACE. [REQUIRED] . DAV:principalname, DAV:displayname, DAV:principal-type: These are the same as the properties that can exist on the principal URI. In this context they are considered 'live.' [OPTIONAL] The DAV:acl element (property) contains 0 or more of the following XML elements: . DAV:ace: A "live" property representing an access control entry, which specifies the set of rights to be either granted or denied to a single principal. The DAV:ace element contains the following XML elements: . DAV:grant: Contains the set of XML elements corresponding to the rights being granted via this ACE. MUST contain at least Clemm,Hopkins,Sedlar [Page 8] INTERNET-DRAFT WebDAV ACL July 14, 2000 one right. MUST NOT be present if the DAV:deny element is present. . DAV:deny: Contains the set of XML elements corresponding to the rights being denied via this ACE. MUST contain at least one right, if present. MUST NOT be present if the DAV:grant element is present. . DAV:principal: Contains information about the principal resource this ACE applies to. [REQUIRED]. . DAV:acepropertytypes: A "live" property containing one or more elements, each of which is an XML tag identifying either a property on this resource or a property on a child resource that may inherit this ACE. Presence of DAV:acepropertytypes distinguishes this ACE as a "Property ACE." The rights associated with a "Property ACE" control access to only the property(ies) contained in DAV:acepropertytypes, and do not control access to the resource as a whole. The set of access rights supported on Property ACEs may be all or a subset of the DAV:access-rights present on this resource. This spec does not provide a mechanism to specify a different set of access-rights for a property, than for the resource. An implementation that supports a different set of access-rights for a property than for the resource, must return an error "Unsupported Right" on an attempt to write a Property ACE with rights not supported by the server. [OPTIONAL] . DAV:inherittochildtype: A "live" property containing one or more elements, each of which is an XML tag identifying the type of child object that will inherit this ACE. This property is only present if DAV:inheritanceflags contains at least one of the following: DAV:inheritonly, DAV:containerinherit, or DAV:objectinherit. A child of the current resource will only inherit this ACE if the type of the child object is present in DAV:inherittochildtype. . DAV:inheritanceflags: A "live" property containing flags indicating the inheritance features of this ACE. For an ACE that is neither inherited, nor inheritable, this element may be either not present, or present but empty. [OPTIONAL] . DAV:inheritancesource: A readonly property containing the URL of the resource from which this ACE was inherited (contained within an DAV:href element). In other words, the ACL on the resource referred to by this URI contains the inheritable explicit ACE which, when propagated to the current resource, resulted in the current ACE. This element may contain the special value of DAV:system-ace to indicate that the ACE is read-only and represents rights granted implicitly by the system. This element may contain the special value of DAV:unknown if the server is unable to generate a valid URI to the resource from which this element was inherited. This element MUST be present if DAV:inheritanceflags contains the Clemm,Hopkins,Sedlar [Page 9] INTERNET-DRAFT WebDAV ACL July 14, 2000 DAV:inherited flag for inherited ACEs and MUST NOT be present for explicit ACEs. The DAV:principal element contains the following elements: . DAV:href: This is a URI representing the resource to which the ACE applies, or one of the special principal identifier tags (e.g., DAV:owner) described in the "Special Principal Identifiers" section of this spec. [REQUIRED] . DAV:principalname, DAV:displayname, DAV:principal-type: These are the same as the properties that can exist on the principal URI. In this context they are considered 'live.' [OPTIONAL] The DAV:inheritanceflags element contains 0 or more of the following XML elements: . DAV:inherited: This flag indicates the ACE is inherited from the ACL on a different resource, identified in DAV:inheritancesource. This flag MUST be present for an inherited ACE and MUST NOT be present for an explicit ACE. This flag must not be present if the DAV:protectaclfrominheritance element is present on this resource unless the DAV:inheritancesource element contains the special value DAV:system-ace, indicating that this ACE wasn't really inherited, but reflects implicit system-granted rights. [REQUIRED] . DAV:inheritonly: This flag indicates the ACE should be ignored during access check. The ACE is present for the purposes of inheritance only and does not affect the security of the current resource. [OPTIONAL] . DAV:containerinherit: This flag indicates that container objects inherit this ACE as an effective ACE. The DAV:inheritonly flag, if also present on this ACE, will be removed from the inherited effective ACE on the container. If the DAV:nopropagateinheritance flag is present on the current ACE, the DAV: containerinherit flag is removed from the inherited ACE on the container. [REQUIRED] . DAV:objectinherit: This flag indicates that non-container resources inherit this ACE as an effective ACE. The DAV:inheritonly flag, if also present on this ACE, will be removed from the inherited effective ACE on the non-container resource. If the DAV:nopropagateinheritance> flag is not present, then container resources will also inherit this ACE with the addition of the DAV:inheritonly> flag. [REQUIRED] . DAV:nopropagateinheritance: This flag indicates the ACE should be inherited one level only. If an object inherits this ACE, the DAV:containerinherit and DAV:objectinherit flags are removed from the resultant inherited ACE, preventing further propagation of this ACE. [OPTIONAL] Clemm,Hopkins,Sedlar [Page 10] INTERNET-DRAFT WebDAV ACL July 14, 2000 The DAV:aclsemantics element MUST contain exactly one of the following XML elements: . DAV:firstspecific: This element is present if the ACL conforms to the FirstSpecific semantics described in this spec. . DAV:explicitdenyprecedence: This element is present if the ACL conforms to the ExplicitDenyPrecedence semantics described in this spec. 4.1 Retrieving Access Control Information Retrieving Access Control information is done via PROPFIND on the resource in question. All ACL properties are also returned as part of the response to PROPFIND allprop request. 4.1.1Example: Retrieving Access Control information The following example shows how access control information could be retrieved using PROPFIND method. Request PROPFIND /top/container/ HTTP/1.1 Host: www.foo.bar Content-type: text/xml; charset="utf-8" Content-Length: 0 Depth: 0 Response HTTP/1.1 207 Multi-Status Content-Type: text/xml Content-Length: xxx HTTP/1.1 200 OK 1997-12-01T17:42:21-08:00 Example collection XXXXX http://www.foo.bar/users/gclemm Geoffrey Clemm Clemm,Hopkins,Sedlar [Page 11] INTERNET-DRAFT WebDAV ACL July 14, 2000 http://www.foo.bar/users/esedlar esedlar Eric Sedlar http://www.foo.bar/groups/marketing Foo.Bar marketing department mktdept http://www.foo.bar/groups/marketing Foo.Bar marketing department mktdept 4.2 Setting Access Control Information An ACL is set by executing a PROPPATCH against the resource that contains the DAV:acl property. An ACL must be written in its entirety. All ACEs (readable by the current user) previously stored in the ACL on the indicated resource are removed. (If the server implements rights outside of those defined in this specification, they might allow only some ACEs to be visible=97 Clemm,Hopkins,Sedlar [Page 12] INTERNET-DRAFT WebDAV ACL July 14, 2000 behaviour on a PROPPATCH is undefined with respect to this specification). Setting an empty ACL property causes all ACEs in the ACL, including ACEs for associated properties, to be deleted. Since permission to set an ACL is typically controlled by a different right from permission to set other properties, it is recommended that ACL-setting PROPPATCHes be executed independently from PROPPATCHes of other properties. PROPATCH as defined in [WEBDAV] is an atomic operation, so failure to set the ACL will result in a failure to set all other properties. [WEBDAV] also defines that operations must be performed from top to bottom, so multiple instances of the DAV:acl element in a single PROPPATCH result in only the last being set. Changing ownership of a resource requires setting the DAV:href element of the DAV:owner property. 4.2.1Example: Setting Access Control information The following example follows from the previous example and changes the group ACE to disallow read access to the ACL for the marketing group. The other information had to be copied from the ACL retrieved in the previous example. Request PROPPATCH /top/container HTTP/1.1 Host: www.foo.bar Content-Type: text/xml Content-Length: xxxx http://www.foo.bar/users/esedlar http://www.foo.bar/groups/marketing Response Clemm,Hopkins,Sedlar [Page 13] INTERNET-DRAFT WebDAV ACL July 14, 2000 HTTP/1.1 207 Multi-Status Content-Type: text/xml Content-Length: xxx http://www.foo.bar/top/container/ HTTP/1.1 200 OK 5 USING ACLS An ACL contains zero or more ACEs that express the rights granted or denied to the principal specified in the ACE. An ACL with zero ACEs implies that no principal is granted any rights. A particular ACE may either grant or deny a set of rights to a single principal. However, since a server may match the currently authenticated HTTP user with multiple principals (for instance, in the case where one principal refers to the user and another principal refers to a group to which the user belongs), it is possible for multiple ACEs to "match" the current user. A user has no access rights to an object protected by an ACL unless that user matches one or more of the principals specified in the ACEs. Server implementations may limit the number of ACEs in an ACL. However, ACL-compliant servers are required to support at least one ACE granting rights to a single principal, and one ACE granting rights to a collection principal. If a client tries to write an ACL containing more ACEs than the server supports, the server should return an error "Too many ACEs." 5.1 System Controlled Rights Some implementations may grant certain rights implicitly. For example, some systems grant the resource owner DAV:readacl and DAV:writeacl implicitly to prevent an ACL from becoming irrevocably locked by an update that grants no one the DAV:writeacl right. Any rights granted implicitly by the system should be reflected as standard ACEs in the ACL returned to the client. Since these implicit permissions are read-only, they should be reflected as "system controlled" ACEs where DAV:inheritanceflags contains DAV:inherited and the DAV:inheritancesource element contains DAV:system-ace. Clemm,Hopkins,Sedlar [Page 14] INTERNET-DRAFT WebDAV ACL July 14, 2000 5.2 Special Principal Identifiers The DAV:principal element in an ACE may contain, instead of a specific security principal identifier, one of the following special tags: . DAV:owner: The principal identified by the owner property on this resource is granted or denied the rights specified in this ACE. . DAV:all: The current user always matches this ACE, whether or not s/he is authenticated. . DAV:authenticated: The current user matches this ACE if authenticated. . DAV:unauthenticated: The current user matches this ACE if not authenticated . DAV:selfprincipal: The current user matches this ACE if the resource (for example, a user information object or security principal account) associated with this ACL is a representation of the current user. 5.3 ACL Semantics Options In order to accommodate the different semantics of multiple existing server implementations, we define a number of ACL Semantics options. The tag associated with each option is used to indicate what semantics to apply to the ACL. A client may use this tag to display information that helps an ACL author understand the implications of his updates. The client must also use this tag to determine the legal semantics for ordering ACEs prior to updating the ACL property. The following ACL Semantics options have been defined to indicate: . restrictions, if any, on the ordering of ACEs within a stored ACL, . how to determine during access check which ACE(s) apply to a user that matches multiple principals, . how to combine the rights granted or denied by multiple matching ACEs during access check. Additional ACL models may be accommodated by defining and registering additional ACL Semantics tags. [How is this done? TBD]. Requested Rights: Some access check algorithms are based on not just the user identity and the ACEs, but also on the "requested rights," which is the set of rights required by the operation for which the access check is being performed. Clemm,Hopkins,Sedlar [Page 15] INTERNET-DRAFT WebDAV ACL July 14, 2000 Effective Rights: The "effective rights" of a user is the set of all rights that would be granted to a user by a given ACL. This set, which is exposed via the DAV:rights property, is independent of any operation "requested rights" and may be generated by a different algorithm than the access check algorithm that determines whether a user has specific requested rights. Each right in the Effective Rights set applies to the user whether the right is requested individually, or in combination with other rights, in the requested rights for an operation. 5.3.1FirstSpecific The FirstSpecific semantic model has the following characteristics: Order of ACEs: ACEs are ordered from "most specific" to "least specific." Typically, the "most specific" ACEs identify principals that refer to a single user. ACEs with "intermediate" specificity have principals that refer to a collection or group of users or other entities. The "least specific" ACEs contain principals, like "World" or "Everyone," that indicate an unbounded set of users. If multiple ACEs with the same level of specificity are present, their order relative to each other is not defined here. Implementations of the FirstSpecific model are unlikely to have multiple ACEs in the intermediate and least specific categories (where multiple ACE matches are possible), making it unimportant to define a rule for relative ordering of ACEs within these two specificity levels. ACE Matching Algorithm: ACEs are evaluated in the order in which they appear in the ACL, from first to last. When a match is found, the algorithm is complete. This first matching ACE alone is used to determine the effective rights of the user. If it is a Grant ACE, then the user is granted all rights in the ACE. If it is a Deny ACE, then the user is denied all rights in the ACE. Requested rights may be compared with the effective rights to determine if access should be granted. ACE Combining Algorithm: The FirstSpecific model never matches more than one ACE to a user, thus there's no need to combine the rights of multiple ACEs. Example Implementation: UNIX rights (rwx for user:group:world) is an example of the FirstSpecific model. 5.3.2ExplicitDenyPrecedence The ExplicitDenyPrecedence model has the following characteristics: Order of ACEs: All Explicit ACEs must precede all Inherited ACEs. Within the group of Explicit ACEs, all Deny ACEs must precede all Grant ACEs. Inherited ACEs are placed in the order in which they are inherited. ACEs inherited from the resource's parent come first, then ACEs from the grandparent, and so on. Clemm,Hopkins,Sedlar [Page 16] INTERNET-DRAFT WebDAV ACL July 14, 2000 ACE Matching and Combining Algorithm: The ACE matching and combining algorithms are not distinct in this model and must be described together. A set of "Granted rights" and a set of "Denied rights", both initialized with zero rights, are maintained in the algorithms to check for Requested Rights and to calculate Effective Rights. In both cases, ACEs are evaluated in the order in which they appear in the ACL, from first to last. Checking for Requested Rights: For each ACE evaluated, if the ACE matches the current user, then: . if it is a Grant ACE, any rights in the ACE that are not already in the "Granted rights" or "Denied rights" sets are added to the "Granted rights" set . if it is a Deny ACE, any rights in the ACE that are not already in the "Granted rights" or "Denied rights" sets are added to the "Denied rights" set If the "Granted rights" set now contains all rights in the set of "requested rights," then no more ACEs are evaluated and the algorithm completes with "Requested Access Granted." If the "Denied rights" set now contains any right that is in the set of "requested rights," then no more ACEs are evaluated and the algorithm completes with "Requested Access Denied." If neither of these cases is true, then the next ACE is evaluated. If there are no more ACEs present in the ACL, then the algorithm completes with "Requested Access Denied" since the accumulated Granted rights did not contain all of the requested rights. Calculating the effective rights of a user: As in the check for requested rights, for each ACE evaluated, if the ACE matches the current user, then: . if it is a Grant ACE, any rights in the ACE that are not already in the "Granted rights" or "Denied rights" sets are added to the "Granted rights" set . if it is a Deny ACE, any rights in the ACE that are not already in the "Granted rights" or "Denied rights" sets are added to the "Denied rights" set If the union of the "Granted rights" and "Denied rights" now contains all possible rights, then no more ACEs are evaluated and the algorithm returns the Granted rights as the set of Effective Rights. Otherwise, the next ACE is evaluated. If there are no more ACEs present in the ACL, then all rights present in the "Granted rights" set are returned as Effective Rights. Example Implementation: Microsoft Windows NT canonical ACLs are an example of this model. Clemm,Hopkins,Sedlar [Page 17] INTERNET-DRAFT WebDAV ACL July 14, 2000 6 ACL INHERITANCE To support a more scalable administration model for configuration of access control information, the spec defines an ACL inheritance model that enables an ACL, or elements of an ACL, to be inherited and reused by other resources. An ACL-compliant implementation is not required to support inheritance. Typically, an ACL defined on a container resource may be inherited by children of that container, grandchildren if they exist, and so on down the tree. Although this hierarchical tree model of inheritance is popular, this spec does not require an implementation's ACL inheritance model to follow a tree structure where child resource inherits from parent resource. Nonetheless, for convenience, this description of inheritance assumes that a child resource would inherit access control information from its parent. 6.1 Inheritable ACEs Access control information is inherited at the granularity of an ACE. An inherited ace is identified by the presence of the DAV:inherited element in the DAV:inheritanceflags property. An "Explicit" ACE is an ACE defined directly on a resource, rather than inherited from a different resource. An ACE without the DAV:inherited element is by definition an Explicit ACE. Only Explicit ACEs may updated by the client. To indicate that an ACE should be inherited by child resources, the DAV:inheritanceflags should contain: . DAV:objectinherit to indicate that non-container children should inherit the ACE, . DAV:containerinherit to indicate that container children should inherit the ACE, or . both to indicate that all child resources should inherit the ACE. 6.2 Updating an inherited ACE When a child resource ACL inherits an ACE, the DAV:inherited flag is present on the ACE to indicate that this ACE is read- only (it may only be edited on the resource where the ACE was explicitly defined). To assist users who want to make changes to the rights that appear in an inherited ACE, the resource from which the ACE was inherited (and therefore, on which the explicit ACE is defined and editable) is identified in the DAV:inheritancesource property. If the inheritance source cannot be determined or if the system is unable to generate a valid URI to the resource from which the ACE was inherited, DAV:inheritancesource contains the special tag DAV:unknown. Clemm,Hopkins,Sedlar [Page 18] INTERNET-DRAFT WebDAV ACL July 14, 2000 6.3 Propagate ACE but do not use for Access Check on this resource In some cases, an ACE (whether explicit or inherited) may be present on a container ACL purely for the sake of propagating the ACE to child objects and NOT to be used for access control on the container itself. In this case, the optional DAV:inheritonly flag is present on the ACE to indicate it should not be used for access check on this container. 6.4 Propagate to immediate children only To indicate that an ACE should be inherited by children, but not by grandchildren or any further down the tree, the optional DAV:nopropagateinheritance flag is present on the ACE. This flag indicates that when this ACE is inherited by child objects, the DAV:objectinherit and/or DAV:containerinherit elements must be removed from the inherited ACE. 6.5 Protect ACL from inheritance To prevent an ACL from inheriting any ACEs, the optional DAV:protectaclfrominheritance property is set on the resource. If this property is present on a resource, the DAV:inherited element must not be present on any ACEs in that resource's ACL. Other inheritance flags may be present on the ACEs of this resource, since this ACL may be the source of inheritable ACEs for the subtree under this resource. Clemm,Hopkins,Sedlar [Page 19] INTERNET-DRAFT WebDAV ACL July 14, 2000 7 XML SCHEMA FOR DEFINED ELEMENTS Clemm,Hopkins,Sedlar [Page 20] INTERNET-DRAFT WebDAV ACL July 14, 2000 8 INTERNATIONALIZATION CONSIDERATIONS To be supplied. 9 SECURITY CONSIDERATIONS To be supplied. 10 SCALABILITY To be supplied. 11 AUTHENTICATION Authentication mechanisms defined in WebDAV will also apply to WebDAV ACL. 12 IANA CONSIDERATIONS This document uses the namespace defined by [RFC2518] for XML elements. All other IANA considerations mentioned in [RFC2518] also applicable to WebDAV ACL. 13 INTELLECTUAL PROPERTY The following notice is copied from RFC 2026, section 10.4, and describes the position of the IETF concerning intellectual property claims made against this document. Clemm,Hopkins,Sedlar [Page 21] INTERNET-DRAFT WebDAV ACL July 14, 2000 The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use other technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. 14 ACKNOWLEDGEMENTS This protocol is the collaborative product of the WebDAV ACL design team: xxx, yyy, zzz. We would like to acknowledge the foundation laid for us by the authors of the WebDAV and HTTP protocols upon which this protocol is layered, and the invaluable feedback from the WebDAV working group. 15 INDEX To be supplied. 16 REFERENCES [RFC2026] S.Bradner, "The Internet Standards Process", Harvard, 1996, . [RFC2068] R.Fielding, J.Gettys, J.C.Mogul, H.Frystyk, and T.Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2068, U.C. Irvine, DEC, MIT/LCS, 1997, . [RFC2119] S.Bradner, "Key words for use in RFCs to Indicate Requirement Levels", Harvard, 1997, . [RFC2518] Y. Goland, E.Whitehead, A.Faizi, S.R.Carter, D.Jensen, "HTTP Extensions for Distributed Authoring - WEBDAV", Microsoft, U.C.Irvine, Netscape, Novell, 1999 . Clemm,Hopkins,Sedlar [Page 22] INTERNET-DRAFT WebDAV ACL July 14, 2000 17 AUTHORS' ADDRESSES Geoffrey Clemm Rational Software 20 Maguire Road Lexington, MA Email: geoffrey.clemm@rational.com Anne Hopkins Microsoft Corporation One Microsoft Way Redmond, WA Email: annehop@microsoft.com Eric Sedlar Oracle Corporation 500 Oracle Parkway Redwood Shores, CA 94065 Email: esedlar@us.oracle.com 18 STILL TO DO : . Describe the interactions with resource locking. I'm not clear what the resolution was as far as locking the ACL separately from locking the resource. . Add a section defining new error codes/messages? Or should we make a pass through the doc and ensure all possible error conditions are mapped to existing errors? . Articulate that the required DAV:principal property should be able to be used for equality checks. Equality checks were mentioned as one reason why this property should be mandatory, even if the URI is fake. . Update "Setting Access Control Information" and to address whether read-only (ie, inherited) ACEs should be stripped out by the client prior to PROPPATCH. Fix, if necessary, comments on editing inherited ACEs in ACL Inheritance section. . Renaming DAV:rights to DAV:effectiverights? and update sample . Revisit description of Property ACEs to reflect group agreement. Add sample code. Anne will need to update Semantics descriptions to address property ACEs. . Update the self, ownergroup stuff according to eventual agreements. . Make document consistent: o Ensure all property descriptions indicate whether the property is: Clemm,Hopkins,Sedlar [Page 23] INTERNET-DRAFT WebDAV ACL July 14, 2000 . "live" or "dead" . read-only or writable . REQUIRED or OPTIONAL o Ensure sample XML exists for all new properties, tags, etc. o Complete empty sections, like Scalability Clemm,Hopkins,Sedlar [Page 24] INTERNET-DRAFT WebDAV ACL July 14, 2000 19 OPEN ISSUES: Issue Description Status 1. Aggregate a right, if granted, that Now addressed in rights grants access to a set of spec. subsidiary rights 2. Rights How do we find out what Now addressed in discovery rights are applicable to a spec. given resource? Can this be done by resource type, to avoid the need to ask each resource this question? 3. Defined Should we define a 'group' Collection list of principal type which principals will "principal- specifically requires that have semantic types" principal membership be meaning (recursive recursive? This might make membership applies) administrative client implementation easier. Should this be a recommendation rather than a requirement? 4. Reserved Is the list of 'reserved' Discussed in 4/28 principals principals complete ( conference call. 'owner', 'all', or Still Open. 'unauthenticated', 'all- authenticated', etc.) 5. Standard Is the list of standard Discussed on rights rights complete? conference call and updated once in draft. 6. XML Do we need to scope the Use DAV namespace, namespace namespace of our XML like other working for ACL elements via , or can we use the regular DAV namespace (shared by both versioning and RFC 2518)? 7. Rights What is the method for Not a method. discovery figuring out the list of DAV:Access-Rights rights? property available. Closed. 8. Multiple Are we sure we don't want to Requires an principals/A allow multiple explicit vote CE [CKNIGHT] principals/ACE? 9. Grant & Are we sure we don't want to Added to spec. Deny allow grant & deny in the Decision reversed Clemm,Hopkins,Sedlar [Page 25] INTERNET-DRAFT WebDAV ACL July 14, 2000 [CKNIGHT] same ACE? Note that this per 6/23 call and simplifies the ACE rule to added to spec 01.3. disallow two ACEs for the Closed. same principal. 10. Semantic Do we need to specify stuff Yes. Added to meaning of like whether or not spec. principal collection principal colls. membership is recursive? [GCLEMM] 11. principa The semantic meaning of Added to spec=97 l-name vs. principal-name should be principal-name display-name defined, or display-name holds [GCLEMM] should be used "authentication" string and displayname holds readable string 12. ChangeOw Can servers disallow PROPPATCH support ner [GCLEMM/ changing the owner? for owner is CKNIGHT] optional in the spec. 13. Local What text is needed Open principal regarding principal URLs URLs without hostname:port 14. ACL as To what extent should ACLs ACLs are properties be treated as properties? properties. Closed. 15. Semantic Would it be more appropriate Open s Model to identify these semantic names models by their [ANNEHOP] implementation names, ie, UNIX, NT Canonical? Could be easier for developers and users. Neither of these models is likely to be re- used by another implementation. 16. Addition Do we need to include Open al Semantics additional ACL semantics models models? What other systems [ANNEHOP] (.htaccess?) do we need to support? 17. Detectin How are WebDAV Access Open g a WebDAV Control compliant servers Access detected? Define acl Control extension for the DAV: server header? [SEANLYND] 18. DAV:user If we're going to be Open /group or treating users as resources, DAV:resource then we should go all the Clemm,Hopkins,Sedlar [Page 26] INTERNET-DRAFT WebDAV ACL July 14, 2000 /collection way. [SEANLYND] 19. Per- ability to specify rights on Open property a per-property basis could ACEs be very useful for webdav. [ANNEHOP] consider adding an optional propertytype-id to the ace? 20. Register Need to describe process for Open ing registering a new ACL Semantics semantics model option. Models [ANNEHOP] 21. Strip Should the client strip all Agreed to strip Inherited Inherited (read-only) ACEs inherited ACEs in ACEs? prior to setting an ACL? Do 6/23 call. Anne [ANNEHOP] we need a flag that re-opening issue. indicates whether the server accepts a client update of inherited ACEs (to support client-side propagation of inheritance)? And/or a flag to indicate that the client WANTs to set inherited ACEs? Clemm,Hopkins,Sedlar [Page 27]