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.Abstract

Authorization is a key function in presence systems. Authorization policies, also known as authorization rules, specify what presence information can be given to which watchers, and when. This

specification defines an Extensible Markup Language (XML) document format for expressing presence authorization rules. Such a document can be manipulated by clients using the XML Configuration Access Protocol (XCAP), although other techniques are permitted.Table of Contents

1. Introduction ....................................................2 2. Terminology .....................................................3 3. Structure of Presence Authorization Documents ...................3 3.1. Conditions .................................................4 3.1.1. Identity ............................................4 3.1.1.1. Acceptable Forms of Authentication .........4 3.1.1.2. Computing a URI for the Watcher ............5 3.1.2. Sphere ..............................................6 3.2. Actions ....................................................7 3.2.1. Subscription Handling ...............................7 3.3. Transformations ............................................9 3.3.1. Providing Access to Data Component Elements .........9 3.3.1.1. Device Information .........................9 3.3.1.2. Person Information ........................10 3.3.1.3. Service Information .......................11 3.3.2. Providing Access to Presence Attributes ............12 3.3.2.1. Provide Activities ........................12 3.3.2.2. Provide Class .............................12 3.3.2.3. Provide DeviceID ..........................13 3.3.2.4. Provide Mood ..............................13 3.3.2.5. Provide Place-is ..........................13

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RFC 5025 Presence Authorization December 2007 3.3.2.6. Provide Place-type ........................13 3.3.2.7. Provide Privacy ...........................13 3.3.2.8. Provide Relationship ......................14 3.3.2.9. Provide Sphere ............................14 3.3.2.10. Provide Status-Icon ......................14 3.3.2.11. Provide Time-Offset ......................14 3.3.2.12. Provide User-Input .......................14 3.3.2.13. Provide Note .............................15 3.3.2.14. Provide Unknown Attribute ................15 3.3.2.15. Provide All Attributes ...................16 4. When to Apply the Authorization Policies .......................17 5. Implementation Requirements ....................................17 6. Example Document ...............................................18 7. XML Schema .....................................................19 8. Schema Extensibility ...........................................21 9. XCAP Usage .....................................................22 9.1. Application Unique ID .....................................22 9.2. XML Schema ................................................22 9.3. Default Namespace .........................................22 9.4. MIME Type .................................................22 9.5. Validation Constraints ....................................22 9.6. Data Semantics ............................................22 9.7. Naming Conventions ........................................23 9.8. Resource Interdependencies ................................23 9.9. Authorization Policies ....................................23 10. Security Considerations .......................................23 11. IANA Considerations ...........................................24 11.1. XCAP Application Usage ID ................................24 11.2. URN Sub-Namespace Registration ...........................25 11.3. XML Schema Registrations .................................25 12. Acknowledgements ..............................................26 13. References ....................................................26 13.1. Normative References .....................................26 13.2. Informative References ...................................271. Introduction

The Session Initiation Protocol (SIP) for Instant Messaging and

Presence (SIMPLE) specifications allow a user, called a watcher, to subscribe to another user, called a presentity [17], in order to

learn their presence information [18]. This subscription is handled by a presence agent. However, presence information is sensitive, and a presence agent needs authorization from the presentity prior to handing out presence information. As such, a presence authorization document format is needed. This specification defines a format for such a document, called a presence authorization document.

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RFC 5025 Presence Authorization December 2007 [8] specifies a framework for representing authorization policies, and is applicable to systems such as geo-location and presence. This framework is used as the basis for presence authorization documents. In the framework, an authorization policy is a set of rules. Each rule contains conditions, actions, and transformations. The

conditions specify under what conditions the rule is to be applied to presence server processing. The actions element tells the server what actions to take. The transformations element indicates how the presence data is to be manipulated before being presented to that watcher, and as such, defines a privacy filtering operation. [8] identifies a small number of specific conditions common to presence and location services, and leaves it to other specifications, such as this one, to fill in usage specific details.

A presence authorization document can be manipulated by clients using several means. One such mechanism is the XML Configuration Access Protocol (XCAP) [2]. This specification defines the details

necessary for using XCAP to manage presence authorization documents.2. Terminology

In this document, the key words \"MUST\

\"SHALL\ and \"OPTIONAL\" are to be interpreted as described in RFC 2119 [1] and indicate requirement levels for compliant implementations.3. Structure of Presence Authorization Documents

A presence authorization document is an XML document, formatted according to the schema defined in [8]. Presence authorization documents inherit the MIME type of common policy documents,

application/auth-policy+xml. As described in [8], this document is composed of rules that contain three parts - conditions, actions, and transformations. Each action or transformation, which is also called a permission, has the property of being a positive grant of

information to the watcher. As a result, there is a well-defined mechanism for combining actions and transformations obtained from several sources. This mechanism is privacy safe, since the lack of any action or transformation can only result in less information being presented to a watcher.

This section defines the new conditions, actions, and transformations defined by this specification.

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RFC 5025 Presence Authorization December 20073.1. Conditions3.1.1. Identity

Although the element is defined in [8], that specification indicates that the specific usages of the framework document need to define details that are protocol and usage specific. In particular, it is necessary for a usage of the common policy framework to: o Define acceptable means of authentication.

o Define the procedure for representing the identity of the WR (Watcher/Requestor) as a URI or Internationalized Resource Identifier (IRI) [13].

This sub-section defines those details for systems based on [18]. It does so in general terms, so that the recommendations defined here apply to existing and future authentication mechanisms in SIP.3.1.1.1. Acceptable Forms of Authentication

When used with SIP, a request is considered authenticated if one of the following is true:

The watcher proves its identity to the server through a form of cryptographic authentication, including authentication based on a shared secret or a certificate, and that authentication yields an identity for the watcher.

The request comes from a sender that is asserting the identity of the watcher, and:

1. the assertion includes a claim that the asserting party used a form of cryptographic authentication (as defined above) to determine the identity of the watcher, and 2. the server trusts that assertion, and

3. the assertion provides an identity in the form of a URI.

Based on this definition, examples of valid authentication techniques include SIP [5], digest authentication [4], cryptographically

verified identity assertions (RFC 4474 [15]), and identity assertions made in closed network environments (RFC 3325 [16]).

However, the anonymous authentication described on page 194 of RFC 3261 [5] is not considered a valid mechanism for authentication

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RFC 5025 Presence Authorization December 2007 because it does not produce an identity for the watcher. However, an anonymous From header field, when used in conjunction with RFC 4474 [15], is considered an acceptable mechanism for authentication, since it still implies that the asserting node performed authentication that produced the identity of the watcher.3.1.1.2. Computing a URI for the Watcher

Computing the URI for the watcher depends on whether the identity is being ascertained through authentication or through an asserted identity.

If an identity assertion is being utilized, the asserted identity itself (which is in the form of a URI for acceptable forms of identity assertion) is utilized as the URI. If the identity

assertion mechanism asserts multiple URIs for the watcher, then each of them is used for the comparisons outlined in [8], and if any of them match a or element, the watcher is considered a match.

If an identity is being determined directly by a cryptographic authentication, that authentication must produce a URI, or must produce some form of identifier that can be linked, through provisioning, to a URI that is bound to that identifier.

For example, in the case of SIP Digest authentication, the

authentication process produces a username scoped within a realm. That username and realm are bound to an Address of Record (AOR) through provisioning, and the resulting AOR is used as the watcher URI. Consider the following \"user record\" in a database: SIP AOR: sip:alice@example.com digest username: ali

digest password: f779ajvvh8a6s6 digest realm: example.com

If the presence server receives a SUBSCRIBE request, challenges it with the realm set to \"example.com\

contains an Authorization header field with a username of \"ali\" and a digest response generated with the password \"f779ajvvh8a6s6\ identity used in matching operations is \"sip:alice@example.com\". In SIP systems, it is possible for a user to have aliases - that is, there are multiple SIP AORs \"assigned\" to a single user. In terms of this specification, there is no relationship between those aliases. Each would look like a different user. This will be the consequence for systems where the watcher is in a different domain than the

presentity. However, even if the watcher and presentity are in the

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RFC 5025 Presence Authorization December 2007 same domain, and the presence server knows that there are aliases for the watcher, these aliases are not mapped to each other or used in any way.

SIP also allows for anonymous requests. If a request is anonymous because the watcher utilized an authentication mechanism that does not provide an identity to the presence server (such as the SIP digest \"anonymous\" username), the request is considered

unauthenticated (as discussed above) and will match only an empty element. If a request is anonymous because it contains a Privacy header field [14], but still contains an asserted identity meeting the criteria defined above, that identity is utilized, and the fact that the request was anonymous has no impact on the identity processing.

It is important to note that SIP frequently uses both SIP URI and tel URI [12] as identifiers, and to make matters more confusing, a SIP URI can contain a phone number in its user part, in the same format used in a tel URI. A WR identity that is a SIP URI with a phone

number will NOT match the and conditions whose ’id’ is a tel URI with the same number. The same is true in the reverse. If the WR identity is a tel URI, this will not match a SIP URI in the or conditions whose user part is a phone number. URIs of different schemes are never equivalent.3.1.2. Sphere

The element is defined in [8]. However, each application making use of the common policy specification needs to determine how the presence server computes the value of the to be used in the evaluation of the condition.

To compute the value of , the presence agent examines all published presence documents for the presentity. If at least one of them includes the element [9] as part of the person data

component [10], and all of those containing the element have the same value for it, which is the value used for the in presence policy processing. If, however, the element was not present in any of the published documents, or it was present but had

inconsistent values, its value is considered undefined in terms of presence policy processing.

Care must be taken in using as a condition for determining the subscription handling. Since the value of changes

dynamically, a state change can cause a subscription to be suddenly terminated. The watcher has no way to know, aside from polling, when their subscription would be reinstated as the value of

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RFC 5025 Presence Authorization December 2007 changes. For this reason, is primarily useful for matching on rules that define transformations.3.2. Actions

3.2.1. Subscription Handling

The element specifies the subscription authorization decision that the server should make. It also specifies whether or not the presence document for the watcher should be constructed using \"polite blocking\". Usage of polite blocking and the subscription authorization decision are specified jointly since proper privacy handling requires a correlation between them. As discussed in [8], since the combination algorithm runs independently for each

permission, if correlations exist between permissions, they must be merged into a single variable. That is what is done here. The element is an enumerated Integer type. The defined values are:

block: This action tells the server to reject the subscription, placing it in the \"terminated\" state. It has the value of zero, and it represents the default value. No value of the element can ever be lower than this. Strictly speaking, it is not necessary for a rule to include an explicit block action, since the default in the absence of any action will be block. However, it is included for completeness.

confirm: This action tells the server to place the subscription in the \"pending\" state, and await input from the presentity to determine how to proceed. It has a value of ten.

polite-block: This action tells the server to place the subscription into the \"active\" state, and to produce a presence document that indicates that the presentity is unavailable. A reasonable

document would exclude device and person information elements, and include only a single service whose basic status is set to closed [3]. This action has a value of twenty.

allow: This action tells the server to place the subscription into the \"active\" state. This action has a value of thirty.

NOTE WELL: Placing a value of block for this element does not

guarantee that a subscription is denied! If any matching rule has any other value for this element, the subscription will receive treatment based on the maximum of those other values. This is based on the combining rules defined in [8].

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RFC 5025 Presence Authorization December 2007 Future specifications that wish to define new types of actions MUST define an entirely new action (separate from ), and define their own set of values for that action. A document could contain both and a subscription handling action

defined by a future specification; in that case, since each action is always a positive grant of information, the resulting action is the least restrictive one across both elements.

The exact behavior of a presence server upon a change in the sub- handling value can be described by utilizing the subscription processing state machine in Figure 1 of RFC 3857 [6].

If the permission changes value to \"block\

causes a \"rejected\" event to be generated into the subscription state machine for all affected subscriptions. This will cause the state machine to move into the \"terminated\" state, resulting in the

transmission of a NOTIFY to the watcher with a Subscription-State header field with value \"terminated\" and a reason of \"rejected\" [7], which terminates their subscription. If a new subscription arrives later on, and the value of that applies to that subscription is \"block\ \"subscribe, policy=reject\" branch from the \"init\" state, and a 403 response to the SUBSCRIBE is generated.

If the permission changes value to \"confirm\ processing depends on the states of the affected subscriptions.

Unfortunately, the state machine in RFC 3857 does not define an event corresponding to an authorization decision of \"pending\". If the subscription is in the \"active\" state, it moves back into the \"pending\" state. This causes a NOTIFY to be sent, updating the Subscription-State [7] to \"pending\". No reason is included in the Subscription-State header field (none are defined to handle this case). No further documents are sent to this watcher. There is no change in state if the subscription is in the \"pending\ or \"terminated\" states. If a new subscription arrives later on, and the value of that applies to that subscription is \"confirm\ policy\" branch from the \"init\" state, and a 202 response to the

SUBSCRIBE is generated, followed by a NOTIFY with Subscription-State of \"pending\". No presence document is included in that NOTIFY. If the permission changes value from \"blocked\" or \"confirm\" to \"polite-block\" or \"allow\ event to be generated into the state machine for all affected

subscriptions. If the subscription was in the \"pending\" state, the state machine will move to the \"active\" state, resulting in the transmission of a NOTIFY with a Subscription-State header field of \"active\

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RFC 5025 Presence Authorization December 2007 If the subscription was in the \"waiting\" state, it will move into the \"terminated\" state. If a new subscription arrives later on, and the value of that applies to that subscription is

\"polite-block\" or \"allow\ \"subscribe, policy=accept\" branch from the \"init\" state, and a 200 OK response to the SUBSCRIBE is generated, followed by a NOTIFY with Subscription-State of \"active\" with a presence document in the body of the NOTIFY.3.3. Transformations

The transformations defined here are used to drive the behavior of the privacy filtering operation. Each transformation defines the visibility a watcher is granted to a particular component of the

presence document. One group of transformations grants visibility to person, device, and service data elements based on identifying information for those elements. Another group of transformations

provides access to particular data elements in the presence document.3.3.1. Providing Access to Data Component Elements

The transformations in this section provide access to person, device, and service data component elements. Once access has been granted to such an element, access to specific presence attributes for that element is controlled by the permissions defined in Section 3.3.2.3.3.1.1. Device Information

The permission allows a watcher to see information present in the presence document. It is a set variable. Each member of the set provides a way to identify a device or group of devices. This specification defines three types of elements in the set - , which identifies a device occurrence by class; , which identifies a device occurrence by device ID; and , which identifies a device occurrence by occurrence ID. The device ID and occurrence ID are defined in [10]. Each member of the set is identified by its type (class, deviceID, or

occurrence-id) and value (value of the class, value of the deviceID, or value of the occurrence-id).

For example, consider the following element:

urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6 biz

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RFC 5025 Presence Authorization December 2007 This set has two members. This is combined with a element from a different rule:

home biz

The result of the set combination (using the union operation) is a set with three elements:

home biz

urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6

The element can also take on the special value , which is a short-hand notation for all device occurrences present in the presence document.

Permission is granted to see a particular device occurrence if one of the device identifiers in the set identifies that device occurrence. If a permission is granted to the watcher, and the of the device occurrence matches the value of the permission based on case-sensitive equality, the device occurrence is included in the presence document. If a permission is granted to the watcher, and the of the device occurrence matches the value of the permission based on URI equivalence, the device occurrence is included in the presence document. If an permission is granted to the watcher, and the

of the device occurrence matches the value of the permission based on case-sensitive equality, the

device occurrence is included in the presence document. In addition, a device occurrence is included in the presence document if the permission was granted to the watcher.3.3.1.2. Person Information

The permission allows a watcher to see the information present in the presence document. It is a set variable. Each member of the set provides a way to identify a person

occurrence. This specification defines two types of elements in the set - , which identifies a person occurrence by class, and

, which identifies an occurrence by its occurrence ID. Each member of the set is identified by its type (class or occurrence-id) and value (value of the class or value of the

occurrence-id). The element can also take on the

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RFC 5025 Presence Authorization December 2007 special value , which is a short-hand notation for all person occurrences present in the presence document. The set

combination is done identically to the element. Permission is granted to see a particular person occurrence if one of the person identifiers in the set identifies that person occurrence. If a permission is granted to the watcher, and the of the person occurrence matches the value of the permission based on case-sensitive equality, the person occurrence is included in the presence document. If an permission is granted to the watcher, and the of the person

occurrence matches the value of the permission based on case-sensitive equality, the person occurrence is included in the presence document. In addition, a person occurrence is included in the presence document if the permission was granted to the watcher.

3.3.1.3. Service Information

The permission allows a watcher to see service information present in elements in the presence document.

Like , it is a set variable. Each member of the set provides a way to identify a service occurrence. This specification defines four types of elements in the set - , which identifies a service occurrence by class; , which identifies a service by its occurrence ID; , which identifies a service by its service URI; and , which

identifies a service by its service URI scheme. Each member of the set is identified by its type (class, occurrence-id, service-uri, or service-uri-scheme) and value (value of the class, value of the occurrence-id, value of the service-uri, or value of the service- uri-scheme). The element can also take on the special value , which is a short-hand notation for all service occurrences present in the presence document. The set combination is done identically to the element. Permission is granted to see a particular service occurrence if one of the service identifiers in the set identifies that service

occurrence. If a permission is granted to the watcher, and the of the service occurrence matches the value of the permission based on case-sensitive equality, the service

occurrence is included in the presence document. If a permission is granted to the watcher, and the of the service occurrence matches the value of the permission based on URI equivalence, the service occurrence is included in the presence document. If an permission is granted to the watcher, and the of the service occurrence

matches the value of the permission based on case-

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RFC 5025 Presence Authorization December 2007 sensitive equality, the service occurrence is included in the

presence document. If a permission is granted to the watcher, and the scheme of the service URI for the service occurrence matches the value of based on case- sensitive equality, the service occurrence is included in the

presence document. In addition, a service occurrence is included in the presence document if the permission was granted to the watcher.

3.3.2. Providing Access to Presence Attributes

The permissions of Section 3.3.1 provide coarse-grained access to presence data by allowing or blocking specific services or devices, and allowing or blocking person information.

Once person, device, or service information is included in the document, the permissions in this section define which presence attributes are reported there. Certain information is always

reported. In particular, the , [9], status, and elements in all elements, if present, are provided to watchers. The element in all elements, if present, is provided to watchers. The and elements in all elements, if present, are provided to all watchers.3.3.2.1. Provide Activities

This permission controls access to the element defined in [9]. The name of the element providing this permission is , and it is a Boolean type. If its value is TRUE, then the element in the person data element is reported to the watcher. If FALSE, this presence attribute is removed if present.3.3.2.2. Provide Class

This permission controls access to the element defined in [9]. The name of the element providing this permission is , and it is a Boolean type. If its value is TRUE, then any element in a person, service, or device data element is reported to the watcher. If FALSE, this presence attribute is removed if present.

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RFC 5025 Presence Authorization December 20073.3.2.3. Provide DeviceID

This permission controls access to the element in a element, as defined in [9]. The name of the element

providing this permission is , and it is a Boolean type. If its value is TRUE, then the element in the service data element is reported to the watcher. If FALSE, this presence attribute is removed if present. Note that the in a device data element is always included, and not controlled by this permission.3.3.2.4. Provide Mood

This permission controls access to the element defined in [9]. The name of the element providing this permission is , and it is a Boolean type. If its value is TRUE, then the element in the person data element is reported to the watcher. If FALSE, this presence attribute is removed if present.3.3.2.5. Provide Place-is

This permission controls access to the element defined in [9]. The name of the element providing this permission is , and it is a Boolean type. If its value is TRUE, then the element in the person data element is reported to the watcher. If FALSE, this presence attribute is removed if present.3.3.2.6. Provide Place-type

This permission controls access to the element defined in [9]. The name of the element providing this permission is , and it is a Boolean type. If its value is TRUE, then the element in the person data element is reported to the watcher. If FALSE, this presence attribute is removed if present.3.3.2.7. Provide Privacy

This permission controls access to the element defined in [9]. The name of the element providing this permission is , and it is a Boolean type. If its value is TRUE, then the element in the person or service data element is reported to the watcher. If FALSE, this presence attribute is removed if present.

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RFC 5025 Presence Authorization December 20073.3.2.8. Provide Relationship

This permission controls access to the element defined in [9]. The name of the element providing this permission is

, and it is a Boolean type. If its value is TRUE, then the element in the service data element is reported to the watcher. If FALSE, this presence attribute is removed if present.3.3.2.9. Provide Sphere

This permission controls access to the element defined in [9]. The name of the element providing this permission is , and it is a Boolean type. If its value is TRUE, then the element in the person data element is reported to the

watcher. If FALSE, this presence attribute is removed if present.3.3.2.10. Provide Status-Icon

This permission controls access to the element defined in [9]. The name of the element providing this permission is

, and it is a Boolean type. If its value is TRUE, then any element in the person or service data element is reported to the watcher. If FALSE, this presence attribute is removed if present.3.3.2.11. Provide Time-Offset

This permission controls access to the element defined in [9]. The name of the element providing this permission is

, and it is a Boolean type. If its value is TRUE, then the element in the person data element is reported to the watcher. If FALSE, this presence attribute is removed if present.

3.3.2.12. Provide User-Input

This permission controls access to the element defined in [9]. The name of the element providing this permission is , and it is an enumerated integer type. Its value defines what information is provided to watchers in person, device, or service data elements:

false: This value indicates that the element is removed from the document. It is assigned the numeric value of 0.

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RFC 5025 Presence Authorization December 2007 bare: This value indicates that the element is to be retained. However, any \"idle-threshold\" and \"since\" attributes are to be removed. This value is assigned the numeric value of 10.

thresholds: This value indicates that the element is to be retained. However, only the \"idle-threshold\" attribute is to be retained. This value is assigned the numeric value of 20. full: This value indicates that the element is to be retained, including any attributes. This value is assigned the numeric value of 30.3.3.2.13. Provide Note

This permission controls access to the element defined in [3] for and [10] for and . The name of the element providing this permission is , and it is a

Boolean type. If its value is TRUE, then any elements in the person, service, or device data elements are reported to the watcher. If FALSE, this presence attribute is removed if present.

This permission has no bearing on any values present within , , , , ,

, or elements. Notes within these elements are essentially values for their respective elements, and are present if the respective element is permitted in the presence document. For example, if an element is present in a presence document, and there is a value for it, that note is present in the document sent to the watcher if the permission is given, regardless of whether the permission is given.

3.3.2.14. Provide Unknown Attribute

It is important that systems be allowed to include proprietary or new presence information and that users be able to set permissions for that information, without requiring an upgrade of the presence server and authorization system. For this reason, the permission is defined. This permission indicates that the unknown presence attribute with the given name and namespace

(supplied as mandatory attributes of the element) should be included in the document. Its type is Boolean. The value of the name attribute MUST be an unqualified element name (meaning that a namespace prefix MUST NOT be included), and the value of the ns attribute MUST be a namespace URI. The two are combined to form a qualified element name, which will be matched to all unknown

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RFC 5025 Presence Authorization December 2007 child elements of the Presence Information Data Format (PIDF)

, , or elements with the same qualified name. In this context, \"unknown\" means that the presence server is not aware of any schemas that define authorization policies for that element. By definition, this will exclude the rule from being applied to any of the presence status extensions defined by RPID, since authorization policies for those are defined here.

Another consequence of this definition is that the interpretation of the element can change should the

presence server be upgraded. For example, consider a server that, prior to the upgrade, had an authorization document that used

with a value of TRUE for some attribute, say foo. This attribute was from a namespace and schema unknown to the server, and so the attribute was provided to watchers. However, after upgrade, the server is now aware of a new namespace and schema for a permission that grants access to the foo attribute. Now, the permission for the foo attribute will be ignored, resulting in a removal of those elements from presence documents sent to watchers. The system remains privacy safe, but behavior might not be as expected. Developers of systems that allow clients to set policies are advised to check the capabilities of the server (using the mechanism described in Section 8) before uploading a new authorization document, to make sure that the behavior will be as expected.

3.3.2.15. Provide All Attributes

This permission grants access to all presence attributes in all of the person, device, and tuple elements that are present in the document (the ones present in the document are determined by the , , and

permissions). It is effectively a macro that expands into a set of provide-activities, provide-class, provide-deviceID, provide-mood, provide-place-is, provide-place-type, provide-privacy, provide- relationship, provide-sphere, provide-status-icon, provide-time- offset, provide-user-input, provide-note, and provide-unknown- attribute permissions such that each presence attribute in the

document has a permission for it. This implies that, so long as an entire person, service, or device occurrence is provided, every single presence attribute, including ones not known to the server and/or defined in future presence document extensions, is granted to the watcher.

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RFC 5025 Presence Authorization December 20074. When to Apply the Authorization Policies

This specification does not mandate at what point in the processing of presence data the privacy filtering aspects of the authorization policy are applied. However, they must be applied such that the final presence document sent to the watcher is compliant to the

privacy policy described in the authorization documents that apply to the user (there can be more than one; the rules for combining them are described in [8]). More concretely, if the presence document sent to a watcher is D, and the privacy filtering operation applied do a presence document x is F(x), then D MUST have the property that D = F(D). In other words, further applications of the privacy

filtering operation would not result in any further changes of the presence document, making further application of the filtering

operation a no-op. A corollary of this is that F(F(D)) = D for all D.

The subscription processing aspects of the document get applied by the server when it decides to accept or reject the subscription.5. Implementation Requirements

The rules defined by the document in this specification form a

\"contract\" of sorts between a client that creates this document and the server that executes the policies it contains. Consequently, presence servers implementing this specification MUST support all of the conditions, actions, and transformations defined in this specification. If servers were to implement a subset of these,

clients would need a mechanism to discover which subset is supported. No such mechanism is defined.

It is RECOMMENDED that clients support all of the actions,

transformations, and conditions defined in this specification. If a client supports a subset, it is possible that a user might manipulate their authorization rules from a different client, supporting a different subset, and store those results on the server. When the user goes back to the first client and views their presence

authorization rules there, the client may not be able to properly

render or manipulate the document retrieved from the server, since it may contain conditions, actions, or transformations not supported by the client. The only reason that this normative requirement is not a MUST is that there are valid conditions in which a user manipulates their presence authorization rules from a single client, in which case this problem does not occur.

This specification makes no normative recommendations on the

mechanism used to transport presence authorization documents from

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RFC 5025 Presence Authorization December 2007 clients to their servers. Although Section 9 defines how to utilize XCAP, XCAP is not normatively required by this specification.6. Example Document

The following presence authorization document specifies permissions for the user \"user@example.com\". The watcher is allowed to access presence information (the ’allow’ value for ). They will be granted access to the presence data of all services whose contact URI schemes are sip and mailto. Person information is also provided. However, since there is no , no device information will be given to the watcher. Within the service and person information provided to the watcher, the element will be shown, as will the element. However, any

\"idle-threshold\" and \"since\" attributes in the element will be removed. Finally, the presence attribute will be shown to the watcher. Any other presence attributes will be removed.

xmlns:cr=\"urn:ietf:params:xml:ns:common-policy\">

allow

sip mailto

true bare ns=\"urn:vendor-specific:foo-namespace\"

name=\"foo\">true

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RFC 5025 Presence Authorization December 20077. XML Schema

xmlns:cr=\"urn:ietf:params:xml:ns:common-policy\" xmlns:pr=\"urn:ietf:params:xml:ns:pres-rules\"

elementFormDefault=\"qualified\" attributeFormDefault=\"unqualified\">

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RFC 5025 Presence Authorization December 2007

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RFC 5025 Presence Authorization December 2007

8. Schema Extensibility

It is anticipated that future changes to this specification are

accomplished through extensions that define new types of permissions. These extensions MUST exist within a different namespace.

Furthermore, the schema defined above and the namespace for elements defined within it MUST NOT be altered by future specifications. Changes in the basic schema, or in the interpretation of elements within that schema, may result in violations of user privacy due to misinterpretation of documents.

When extensions are made to the set of permissions, it becomes necessary for the agent constructing the permission document

(typically a SIP user agent, though not necessarily) to know which permissions are supported by the server. This allows the agent to know how to build a document that results in the desired behavior, since unknown permissions would be ignored by the server. To handle this, when presence authorization documents are transported using

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RFC 5025 Presence Authorization December 2007 XCAP, the XCAP capabilities document stored at the server SHOULD

contain the namespaces for the permissions supported by the presence server. This way, an agent can query for this list prior to constructing a document.9. XCAP Usage

The following section defines the details necessary for clients to manipulate presence authorization documents from a server using XCAP.9.1. Application Unique ID

XCAP requires application usages to define a unique application usage ID (AUID) in either the IETF tree or a vendor tree. This

specification defines the \"pres-rules\" AUID within the IETF tree, via the IANA registration in Section 11.9.2. XML Schema

XCAP requires application usages to define a schema for their

documents. The schema for presence authorization documents is in Section 7.

9.3. Default Namespace

XCAP requires application usages to define the default namespace for their URIs. The default namespace is urn:ietf:params:xml:ns:pres- rules.9.4. MIME Type

XCAP requires application usages to define the MIME type for

documents they carry. Presence authorization documents inherit the MIME type of common policy documents, application/auth-policy+xml.9.5. Validation Constraints

There are no additional constraints defined by this specification.9.6. Data Semantics

Semantics of a presence authorization document are discussed in Section 3.

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RFC 5025 Presence Authorization December 20079.7. Naming Conventions

When a presence agent receives a subscription for some user foo

within a domain, it will look for all documents within http://[xcap root]/pres-rules/users/foo, and use all documents found beneath that point to guide authorization policy. If only a single document is used, it SHOULD be called \"index\".9.8. Resource Interdependencies

There are no additional resource interdependencies defined by this application usage.

9.9. Authorization Policies

This application usage does not modify the default XCAP authorization policy, which is that only a user can read, write, or modify their own documents. A server can allow privileged users to modify

documents that they don’t own, but the establishment and indication of such policies are outside the scope of this document.10. Security Considerations

Presence authorization policies contain very sensitive information. They indicate which other users are \"liked\" or \"disliked\" by a user. As such, when these documents are transported over a network, they SHOULD be encrypted.

Modification of these documents by an attacker can disrupt the service seen by a user, often in subtle ways. As a result, when these documents are transported, the transport SHOULD provide authenticity and message integrity.

In the case where XCAP is used to transfer the document, both clients and servers MUST implement HTTP over Transport Layer Security (TLS) and HTTP Digest authentication. Sites SHOULD authenticate clients using digest authentication over TLS, and sites SHOULD define the root services URI as an https URI.

Authorization documents themselves exist for the purposes of providing a security function - privacy. The SIP presence

specifications [18] require the usage of an authorization function prior to the granting of presence information, and this specification meets that need. Presence authorization documents inherit the privacy properties of the common policy format on which they are

based. This format has been designed to be privacy-safe, which means that failure of the presence server to obtain or understand an authorization document can never reveal more information than is

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RFC 5025 Presence Authorization December 2007 desired about the user, only less. This is a consequence of the fact that all permissions are positive grants of information, and not negative grants.

A consequence of this design is that the results of combining several authorization documents can be non-obvious to end users. For example, if one authorization document grants permission for all

users from the example.com domain to see their presence, and another document blocks joe@example.com, the combination of these will still provide presence to joe@example.com. Designers of user interfaces are encouraged to carefully pay attention to the results of combining multiple rules.

Another concern is cases where a user sets their privacy preferences from one client, uploads their presence authorization document to a server, and then modifies them from a different client. If the

clients support different subsets of the document format, users may be confused about what information is being revealed. Clients retrieving presence authorization documents from a server SHOULD render, to the users, information about rules that they do not understand, so that users can be certain what rules are in place.11. IANA Considerations

There are several IANA considerations associated with this specification.

11.1. XCAP Application Usage ID

This section registers an XCAP Application Usage ID (AUID) according to the IANA procedures defined in [2]. Name of the AUID: pres-rules

Description: Presence rules are documents that describe the

permissions that a presentity [17] has granted to users that seek to watch their presence.

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RFC 5025 Presence Authorization December 200711.2. URN Sub-Namespace Registration

This section registers a new XML namespace, per the guidelines in [11]

URI: The URI for this namespace is urn:ietf:params:xml:ns:pres-rules.

Registrant Contact: IETF, SIMPLE working group (simple@ietf.org), Jonathan Rosenberg (jdrosen@jdrosen.net). XML: BEGIN

content=\"text/html;charset=iso-8859-1\"/>

Namespace for Permission Statements

urn:ietf:params:xml:ns:pres-rules

See RFC5025.

11.3. XML Schema Registrations

This section registers an XML schema per the procedures in [11]. URI: urn:ietf:params:xml:schema:pres-rules.

Registrant Contact: IETF, SIMPLE working group (simple@ietf.org), Jonathan Rosenberg (jdrosen@jdrosen.net).

The XML for this schema can be found as the sole content of Section 7.

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RFC 5025 Presence Authorization December 200712. Acknowledgements

The author would like to thank Richard Barnes, Jari Urpalainen, Jon Peterson, and Martin Hynar for their comments.13. References

13.1. Normative References

[1] Bradner, S., \"Key words for use in RFCs to Indicate Requirement Levels\

[2] Rosenberg, J., \"The Extensible Markup Language (XML)

Configuration Access Protocol (XCAP)\ [3] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and J. Peterson, \"Presence Information Data Format (PIDF)\ 3863, August 2004.

[4] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,

Leach, P., Luotonen, A., and L. Stewart, \"HTTP Authentication: Basic and Digest Access Authentication\ [5] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M., and E. Schooler, \"SIP: Session Initiation Protocol\

[6] Rosenberg, J., \"A Watcher Information Event Template-Package for the Session Initiation Protocol (SIP)\ [7] Roach, A., \"Session Initiation Protocol (SIP)-Specific Event Notification\

[8] Schulzrinne, H., Tschofenig, H., Morris, J., Cuellar, J., Polk, J., and J. Rosenberg, \"Common Policy: A Document Format for Expressing Privacy Preferences\

[9] Schulzrinne, H., Gurbani, V., Kyzivat, P., and J. Rosenberg,

\"RPID: Rich Presence Extensions to the Presence Information Data Format (PIDF)\

[10] Rosenberg, J., \"A Data Model for Presence\ [11] Mealling, M., \"The IETF XML Registry\ 2004.

[12] Schulzrinne, H., \"The tel URI for Telephone Numbers\ December 2004.

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RFC 5025 Presence Authorization December 2007 [13] Duerst, M. and M. Suignard, \"Internationalized Resource Identifiers (IRIs)\

[14] Peterson, J., \"A Privacy Mechanism for the Session Initiation Protocol (SIP)\13.2. Informative References

[15] Peterson, J. and C. Jennings, \"Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)\ RFC 4474, August 2006.

[16] Jennings, C., Peterson, J., and M. Watson, \"Private Extensions to the Session Initiation Protocol (SIP) for Asserted Identity within Trusted Networks\

[17] Day, M., Rosenberg, J., and H. Sugano, \"A Model for Presence and Instant Messaging\

[18] Rosenberg, J., \"A Presence Event Package for the Session Initiation Protocol (SIP)\Author’s Address Jonathan Rosenberg Cisco

Edison, NJ US

EMail: jdrosen@cisco.com

URI: http://www.jdrosen.net

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RFC 5025 Presence Authorization December 2007Full Copyright Statement

Copyright (C) The IETF Trust (2007).

This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.

This document and the information contained herein are provided on an \"AS IS\" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property

The IETF takes no position regarding the validity or scope of any

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Copies of IPR disclosures made to the IETF Secretariat 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

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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 implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org.

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