SIMPLE J. Rosenberg
Internet-Draft Cisco Systems
Expires: January 19, 2006 July 18, 2005
Presence Authorization Rules
draft-ietf-simple-presence-rules-03
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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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Structure of Presence Authorization Documents . . . . . . . 4
3.1 Conditions . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.1 Identity . . . . . . . . . . . . . . . . . . . . . . . 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 Device ID . . . . . . . . . . . . . . . . 13
3.3.2.4 Provide Mood . . . . . . . . . . . . . . . . . . . 13
3.3.2.5 Provide Place-is . . . . . . . . . . . . . . . . . 13
3.3.2.6 Provide Place-type . . . . . . . . . . . . . . . . 13
3.3.2.7 Provide Privacy . . . . . . . . . . . . . . . . . 13
3.3.2.8 Provide Relationship . . . . . . . . . . . . . . . 13
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 . . . . . . . . . . 16
5. Example Document . . . . . . . . . . . . . . . . . . . . . . 16
6. XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . 17
7. Schema Extensibility . . . . . . . . . . . . . . . . . . . . 20
8. XCAP Usage . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.1 Application Unique ID . . . . . . . . . . . . . . . . . . 20
8.2 Structure of Permission Statements . . . . . . . . . . . . 20
8.3 Additional Constraints . . . . . . . . . . . . . . . . . . 20
8.4 Naming Conventions . . . . . . . . . . . . . . . . . . . . 20
8.5 Authorization Policies . . . . . . . . . . . . . . . . . . 20
8.6 XML Schema . . . . . . . . . . . . . . . . . . . . . . . . 21
9. Security Considerations . . . . . . . . . . . . . . . . . . 21
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 21
10.1 XCAP Application Usage ID . . . . . . . . . . . . . . . 21
10.2 URN Sub-Namespace Registration . . . . . . . . . . . . . 21
10.3 XML Schema Registrations . . . . . . . . . . . . . . . . 22
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
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11.1 Normative References . . . . . . . . . . . . . . . . . . 22
11.2 Informative References . . . . . . . . . . . . . . . . . 24
Author's Address . . . . . . . . . . . . . . . . . . . . . . 24
Intellectual Property and Copyright Statements . . . . . . . 25
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1. 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 [19], in order to
learn their presence information [22]. 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.
[12] 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. [12]
identifies a small number of specific conditions, actions and
permissions 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", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
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 [12]. Presence authorization
documents inherit the MIME type of common policy documents,
application/auth-policy+xml. As described in [12], this document is
composed of 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.
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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.
3.1 Conditions
3.1.1 Identity
Although the <identity> element is defined in [12], 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 neccesary for a usage of the common policy
framework to:
o Define how authentication mechanisms for the protocol produce
identities of the form user@domain.
o Define whether those identities are authenticated,
unauthenticated, or asserted.
This sub-section defines those details for systems based on [22].
For requests that are authenticated using SIP [9] digest
authentication [8], the identity of the watcher is set equal to the
user and domain part of the SIP Address of Record (AOR) for the user
that has authenticated themselves. For example, consider the
following "user record":
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", and the subsequent SUBSCRIBE
contains an Authorization header field with a username of "ali" and a
digest response generated with the password "f779ajvvh8a6s6", the
identity used in matching operations is "sip:alice@example.com".
Identities obtained through digest authentication are considered
"authenticated identities" according to the common policy framework.
For requests that are authenticated using RFC 3325 [23], the identity
is equal to the username and domain parts of the SIP URI in the
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P-Asserted-ID header field. These identities are considered
"asserted identities" according to the common policy framework. If
the P-Asserted-ID header field only contains a tel URI [18], it is
not possible to obtain an identity of the form user@domain. As such,
the identity for such requests is considered undefined, and thus
equivalent to an unauthenticated identity.
For requests that are authenticated using the SIP Identity mechanism
[14], the common policy identity is equal to the username and domain
part of the URI in the From header field of the request, assuming
that the signature in the Identity header field has been validated.
These identities are considered "asserted identities" according to
the common policy framework.
In SIP systems, it is possible for a user to have aliases - that is,
there are multiple SIP AOR "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 were the watcher is in a different domain than the
presentity. However, even if the watcher and presentity are in the
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. The request is considered
anonymous if it was authenticated by the presence server using the
<anonymous> username defined in RFC 3261, if the asserted identity
[23] has a URI in the "anonymous.invalid" domain [17], or if the From
field has a username of anonymous within some domain, and the
Identity header field is present with a valid signature provided by
that domain [14]. The common policy framework does not have any
support for anonymous identities. As such, if a SIP request is
anonymous, it is equivalent to unauthenticated as far as the common
policy framework.
3.1.2 Sphere
The <sphere> element is defined in [12]. However, each application
making use of the common policy specification needs to determine how
the presence server computes the value of the sphere to be used in
the evaluation of the condition.
To compute the value of <sphere>, the presence agent examines all
published presence documents for the presentity. If at least one of
them include the <sphere> element [13] as part of the person data
component [15], and all of those containing the element have the same
value for it, that is the value used for the sphere in common policy
processing. If, however, the <sphere> element was not present in any
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of the published documents, or it was present but had inconsistent
values, its value is considered undefined in terms of common policy
processing.
Care must be taken in using <sphere> as a condition for determining
the subscription handling. Since the value of <sphere> 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 re-instated as the value of <sphere>
changes. For this reason, <sphere> is primarily useful for matching
on rules that define transformations.
3.2 Actions
3.2.1 Subscription Handling
The <sub-handling> 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" or not. Usage of polite blocking and the
subscription authorization decision are specified jointly since
proper privacy handling requires a correlation between them. As
discussed in [12], 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 <sub-handling> element is an enumerated Integer type. The
defined values are:
block: This action tells the server to place the subscription in the
rejected state. It has the value of zero, and it represents the
default value. No value of the sub-handling element can ever be
lower than this. Strictly speaking, it is not necessary to every
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 one.
polite-block: This action tells the server to place the subscription
into the "accepted" 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 two.
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allow: This action tells the server to place the subscription into
the "accepted" state. This action has a value of three.
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 [12].
Future specifications can define additional values for this
permission, allowing for the selection of other composition policies.
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 [10]. Each
subscription is associated with a set of permissions that represents
the combination of all permissions that apply to that subscription,
using the combining rules in [12].
If the sub-handling permission changes value to "block", this 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" [11],
which terminates their subscription. If a new subscription arrives
later on, and the value of sub-handling that applies to that
subscription is "block", the subscription processing follows the
"subscribe, policy=reject" branch from the init state, and a 403
response to the SUBSCRIBE is generated.
If the sub-handling permission changes value to confirm, the
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 [11] 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, waiting or terminated
states. If a new subscription arrives later on, and the value of
sub-handling that apples to that subscription is "pending", the
subscription processing follows the "subscribe, no 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.
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If the sub-handling permission changes value to "polite-block" or
"allow", this causes an "approved" event to be generated into the
state machine for all affected subscriptions. This will cause the
machine to move into the active state if it is currently in pending,
resulting in the transmission of a NOTIFY with a Subscription-State
header field of "active", and the inclusion of a presence document in
that NOTIFY. If a new subscription arrives later on, and the value
of sub-handling that applies to that subscription is is "polite-
block" or "allow", the subscription processing follows the
"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 grant visibility to
person, device and service data elements based on identifying
information for those elements. Another group of transformations
provide 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 <provide-devices> permission allows a watcher to see <device>
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 - <class>, which identifies a device occurrence by class,
<device-id>, which identifies a device occurrence by device ID, and
<occurrence-id>, which identifies a device occurrence by occurrence
ID. Each member of the set is identified by its type (class,
device-id or occurrence-id) and value (value of the class, value of
the device-id, or value of the occurrence-id).
For example, consider the following <provide-devices> element:
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<provide-devices>
<device-id>urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6</device-id>
<class>biz</class>
</provide-devices>
This set has two members. This is combined with a <provide-devices>
element from a different rule:
<provide-devices>
<class>home</class>
<class>biz</class>
</provide-devices>
The result of the set combination (using the union operation) is a
set with four elements:
<provide-devices>
<class>home</class>
<class>biz</class>
<device-id>urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6</device-id>
</provide-devices>
The <provide-devices> element can also take on the special value
<all-devices> 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 <class> permission is granted to the watcher, and the <class> of
the device occurrence matches the value of the <class> permission
based on case sensitive equality, the device occurrence is included
in the presence document. If a <device-id> permission is granted to
the watcher, and the <device-id> of the device occurrence matches the
value of the <device-id> permission based on URI equivalence, the
device occurrence is included in the presence document. If a
<occurrence-id> permission is granted to the watcher, and the
<occurrence-id> of the device occurrence matches the value of the
<occurrence-id> 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 <all-
devices> permission was granted to the watcher.
3.3.1.2 Person Information
The <provide-persons> permission allows a watcher to see the <person>
information present in the presence document. It is a set variable.
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Each member of the set provides a way to identify a person
occurrence. This specification defines two types of elements in the
set - <class>, which identifies a person occurrence by class, and
<occurrence-id>, 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 <provide-persons> element can also take on the
special value <all-persons> which is a short-hand notation for all
person occurrences present in the presence document. The set
combination is done identically to the <provide-devices> 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 <class> permission is granted to the watcher, and the <class> of
the person occurrence matches the value of the <class> permission
based on case sensitive equality, the person occurrence is included
in the presence document. If a <occurrence-id> permission is granted
to the watcher, and the <occurrence-id> of the person occurrence
matches the value of the <occurrence-id> 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 <all-persons> permission was granted to the
watcher.
3.3.1.3 Service Information
The <provide-services> permission allows a watcher to see service
information present in <tuple> elements in the presence document.
Like <provide-devices>, 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 - <class>, which identifies
a service occurrence by class, <occurrence-id>, which identifies a
service by its occurrence ID, <service-uri>, which identifies a
service by its service URI, and <service-uri-scheme>, 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 <provide-services> element can also take on the
special value <all-services> which is a short-hand notation for all
service occurrences present in the presence document. The set
combination is done identically to the <provide-persons> 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 <class> permission is granted to the watcher, and
the <class> of the service occurrence matches the value of the
<class> permission based on case sensitive equality, the service
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occurrence is included in the presence document. If a <service-uri>
permission is granted to the watcher, and the <service-uri> of the
service occurrence matches the value of the <service-uri> permission
based on URI equivalence, the service occurrence is included in the
presence document. If a <occurrence-id> permission is granted to the
watcher, and the <occurrence-id> of the service occurrence matches
the value of the <occurrence-id> permission based on case sensitive
equality, the service occurrence is included in the presence
document. If a <service-uri-scheme> permission is granted to the
watcher, and the scheme of the service URI for the service occurrence
matches the value of <service-uri-scheme> 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 <all-services> 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 <contact>, <service-class> [13],
<basic> status and <timestamp> elements in all <tuple> elements, if
present, are provided to watchers . The <timestamp> element in all
<person> elements, if present, is provided to watchers. The
<timestampt> and <device-id> elements in all <device> elements, if
present, is provided to all watchers.
3.3.2.1 Provide Activities
This permission controls access to the <activities> element defined
in [13]. The name of the element providing this permission is
<provide-activities>, and it is a boolean type. If its value is
TRUE, then the <activities> 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 <class> element defined in
[13]. The name of the element providing this permission is <provide-
class>, and it is a boolean type. If its value is TRUE, then the
<class> element in the person, service or device data element is
reported to the watcher. If FALSE, this presence attribute is
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removed if present.
3.3.2.3 Provide Device ID
This permission controls access to the <device-id> element defined in
[13]. The name of the element providing this permission is <provide-
device-id>, and it is a boolean type. If its value is TRUE, then the
<device-id> element in the service data element is reported to the
watcher. If FALSE, this presence attribute is removed if present.
3.3.2.4 Provide Mood
This permission controls access to the <mood> element defined in
[13]. The name of the element providing this permission is <provide-
mood>, and it is a boolean type. If its value is TRUE, then the
<mood> 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 <place-is> element defined in
[13]. The name of the element providing this permission is <provide-
place-is>, and it is a boolean type. If its value is TRUE, then the
<place-is> 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 <place-type> element defined
in [13]. The name of the element providing this permission is
<provide-place-type>, and it is a boolean type. If its value is
TRUE, then the <place-type> 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 <privacy> element defined in
[13]. The name of the element providing this permission is <provide-
privacy>, and it is a boolean type. If its value is TRUE, then the
<privacy> element in the service data element is reported to the
watcher. If FALSE, this presence attribute is removed if present.
3.3.2.8 Provide Relationship
This permission controls access to the <relationship> element defined
in [13]. The name of the element providing this permission is
<provide-relationship>, and it is a boolean type. If its value is
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TRUE, then the <relationship> 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 <sphere> element defined in
[13]. The name of the element providing this permission is <provide-
sphere>, and it is a boolean type. If its value is TRUE, then the
<sphere> 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 <status-icon> element defined
in [13]. The name of the element providing this permission is
<provide-status-icon>, and it is a boolean type. If its value is
TRUE, then any <status-icon> 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 <time-offset> element defined
in [13]. The name of the element providing this permission is
<provide-time-offset>, and it is a boolean type. If its value is
TRUE, then the <time-offset> 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 <user-input> element defined
in [13]. The name of the element providing this permission is
<provide-user-input>, and it is an enumerated integer type. Its
value defines what information is provided to watchers:
false: This value indicates that the <user-input> element is removed
from the document. It is assigned the numeric value of 0.
bare: This value indicates that the <user-input> element is to be
retained. However, any "idle-threshold" and "since" attributes
are to be removed. This value is assigned the numeric value of 1.
thresholds: This value indicates that the <user-input> element is to
be retained. However, only the "idle-threshold" attribute is to
be retained. This value is assigned to the numeric value of 2.
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full: This value indicates that the <user-input> element is to be
retained, including any attributes. This value is assigned to the
numeric value of 3.
3.3.2.13 Provide Note
This permission controls access to the <note> element defined in [3]
for <tuple> and [15] for <person> and <device>. The name of the
element providing this permission is <provide-note>, and it is a
boolean type. If its value is TRUE, then the <note> elements in the
person, service or device data elements are reported to the watcher.
If FALSE, this presence attribute is removed if present.
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 <provide-unknown-
attribute> permission is defined. This permission indicates that the
unknown presence attribute with the given name (supplied as mandatory
attribute of the <provide-unknown-attribute> element) should be
included in the document. Its type is boolean.
The value of the name attribute MUST be a qualified element name
(meaning that the namespace prefix MUST be included), which will be
matched to all unknown child elements of the PIDF <tuple>, <device>
or <person< elements with the same qualified name. The namespace
bindings are taken from those in scope at the point in the document
where the <provide-unknown-attribute> is present. 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 <provide-unknown-attribute> rule from being
applied to any of the presence status extensions defined by RPID.
Another consequence of this definition is that the interpretation of
the <provide-unknown-attribute> element can change should the
presence server be upgraded with a new schema that defines
authorization rules for elements included in a <provide-unknown-
attribute>. The <provide-unknown-attribute> permissions for those
elements will then 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 which allow clients to set policies are advised
to check the capabilities of the server, as defined in [21], before
uploading a new authorization document, to make sure that the
behavior will be as expected.
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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 determedined by the
<provide-persons>, <provide-devices> and <provide-services>
permissions). It is effectively a macro that expands into a set of
provide-activities, provide-class, provide-device-id, 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.
4. 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 document. More concretely, if the
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). 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. Example Document
The following presence authorization document specifies permissions
for the user "user@example.com".
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<?xml version="1.0" encoding="UTF-8"?>
<cr:ruleset xmlns="urn:ietf:params:xml:ns:pres-rules"
xmlns:cr="urn:ietf:params:xml:ns:common-policy"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:new="urn:vendor-specific:foo-namespace"
xsi:schemaLocation="urn:ietf:params:xml:ns:pres-rules pres-rules.xsd">
<cr:rule id="1">
<cr:conditions>
<cr:identity>
<cr:id entity="user@example.com"/>
</cr:identity>
</cr:conditions>
<cr:actions>
<sub-handling>allow</sub-handling>
</cr:actions>
<cr:transformations>
<provide-services>
<service-uri-scheme>sip</service-uri-scheme>
<service-uri-scheme>mailto</service-uri-scheme>
</provide-services>
<provide-persons>
<all-persons/>
</provide-persons>
<provide-activities>true</provide-activities>
<provide-user-input>bare</provide-user-input>
<provide-unknown-attribute name="new:foo">true</provide-unknown-attribute>
</cr:transformations>
</cr:rule>
</cr:ruleset>
6. XML Schema
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:cr="urn:ietf:params:xml:ns:common-policy"
xmlns:pr="urn:ietf:params:xml:ns:pres-rules"
targetNamespace="urn:ietf:params:xml:ns:pres-rules"
elementFormDefault="qualified" attributeFormDefault="unqualified">
<xs:import namespace="urn:ietf:params:xml:ns:common-policy"/>
<xs:simpleType name="booleanPermission">
<xs:restriction base="xs:boolean"/>
</xs:simpleType>
<xs:element name="service-uri-scheme" type="xs:token"/>
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<xs:element name="class" type="xs:token"/>
<xs:element name="occurrence-id" type="xs:token"/>
<xs:element name="service-uri" type="xs:anyURI"/>
<xs:complexType name="provideServicePermission">
<xs:choice>
<xs:element name="all-services">
<xs:complexType/>
</xs:element>
<xs:sequence minOccurs="0" maxOccurs="unbounded">
<xs:choice>
<xs:element ref="pr:service-uri"/>
<xs:element ref="pr:service-uri-scheme"/>
<xs:element ref="pr:occurrence-id"/>
<xs:element ref="pr:class"/>
<xs:any namespace="##other"/>
</xs:choice>
</xs:sequence>
</xs:choice>
</xs:complexType>
<xs:element name="provide-services"
type="pr:provideServicePermission"/>
<xs:element name="device-id" type="xs:anyURI"/>
<xs:complexType name="provideDevicePermission">
<xs:choice>
<xs:element name="all-devices">
<xs:complexType/>
</xs:element>
<xs:sequence>
<xs:choice>
<xs:element ref="pr:device-id"/>
<xs:element ref="pr:occurrence-id"/>
<xs:element ref="pr:class"/>
<xs:any namespace="##other"/>
</xs:choice>
</xs:sequence>
</xs:choice>
</xs:complexType>
<xs:element name="provide-devices"
type="pr:provideDevicePermission"/>
<xs:complexType name="providePersonPermission">
<xs:choice>
<xs:element name="all-persons">
<xs:complexType/>
</xs:element>
<xs:sequence>
<xs:choice>
<xs:element ref="pr:occurrence-id"/>
<xs:element ref="pr:class"/>
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<xs:any namespace="##other"/>
</xs:choice>
</xs:sequence>
</xs:choice>
</xs:complexType>
<xs:element name="provide-persons" type="pr:providePersonPermission"/>
<xs:element name="provide-activities" type="pr:booleanPermission"/>
<xs:element name="provide-class" type="pr:booleanPermission"/>
<xs:element name="provide-device-id" type="pr:booleanPermission"/>
<xs:element name="provide-mood" type="pr:booleanPermission"/>
<xs:element name="provide-place-is" type="pr:booleanPermission"/>
<xs:element name="provide-place-type" type="pr:booleanPermission"/>
<xs:element name="provide-privacy" type="pr:booleanPermission"/>
<xs:element name="provide-relationship" type="pr:booleanPermission"/>
<xs:element name="provide-status-icon" type="pr:booleanPermission"/>
<xs:element name="provide-sphere" type="pr:booleanPermission"/>
<xs:element name="provide-time-offset" type="pr:booleanPermission"/>
<xs:element name="provide-user-input">
<xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="false"/>
<xs:enumeration value="bare"/>
<xs:enumeration value="thresholds"/>
<xs:enumeration value="full"/>
</xs:restriction>
</xs:simpleType>
</xs:element>
<xs:element name="provide-note" type="pr:booleanPermission"/>
<xs:simpleType name="componentIDPermission">
<xs:restriction base="xs:token">
<xs:enumeration value="randomize"/>
<xs:enumeration value="obfuscate"/>
<xs:enumeration value="allow"/>
</xs:restriction>
</xs:simpleType>
<xs:complexType name="unknownBooleanPermission">
<xs:simpleContent>
<xs:extension base="pr:booleanPermission">
<xs:attribute name="name" type="xs:string" use="required"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
<xs:element name="provide-unknown-attribute"
type="pr:unknownBooleanPermission"/>
<xs:element name="provide-all-attributes">
<xs:complexType/>
</xs:element>
</xs:schema>
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7. 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
mis-interpretation of documents.
This specification also defines two substitution groups. One is for
service identifiers, and one is for device identifiers. It is
expected that future extensions will specify new ways of identifying
services and devices for inclusion in a document. These new
permissions MUST be assigned to this substitution group.
8. XCAP Usage
The following section defines the details necessary for clients to
manipulate presence authorization documents from a server using XCAP.
8.1 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 10.
8.2 Structure of Permission Statements
The structure of permission statements is defined in Section 3.
8.3 Additional Constraints
There are no additional constraints defined by this specification.
8.4 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.
8.5 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
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documents. A server can allow priveleged users to modify documents
that they don't own, but the establishment and indication of such
policies is outside the scope of this document.
8.6 XML Schema
The XML schema is defined in Section 6.
9. 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, clients
SHOULD use HTTP over TLS, and servers SHOULD define the root services
URI as an https URI. The server SHOULD authenticate the client over
the resulting TLS connection using HTTP digest.
10. IANA Considerations
There are several IANA considerations associated with this
specification.
10.1 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 [19] has granted to users that seek
to watch their presence.
10.2 URN Sub-Namespace Registration
This section registers a new XML namespace, per the guidelines in
[16]
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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
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Presence Rules Namespace</title>
</head>
<body>
<h1>Namespace for Permission Statements</h1>
<h2>urn:ietf:params:xml:ns:pres-rules</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
10.3 XML Schema Registrations
This section registers an XML schema per the procedures in [16].
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 6.
11. References
11.1 Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
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[2] Rosenberg, J., "The Extensible Markup Language (XML)
Configuration Access Protocol (XCAP)",
draft-ietf-simple-xcap-07 (work in progress), June 2005.
[3] Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W., and
J. Peterson, "Presence Information Data Format (PIDF)",
RFC 3863, August 2004.
[4] Bray, T., Paoli, J., Sperberg-McQueen, C., and E. Maler,
"Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
FirstEdition REC-xml-20001006, October 2000.
[5] Moats, R., "URN Syntax", RFC 2141, May 1997.
[6] Murata, M., St. Laurent, S., and D. Kohn, "XML Media Types",
RFC 3023, January 2001.
[7] Moats, R., "A URN Namespace for IETF Documents", RFC 2648,
August 1999.
[8] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication:
Basic and Digest Access Authentication", RFC 2617, June 1999.
[9] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[10] Rosenberg, J., "A Watcher Information Event Template-Package
for the Session Initiation Protocol (SIP)", RFC 3857,
August 2004.
[11] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[12] Schulzrinne, H., "A Document Format for Expressing Privacy
Preferences", draft-ietf-geopriv-common-policy-04 (work in
progress), February 2005.
[13] Schulzrinne, H., "RPID: Rich Presence Extensions to the
Presence Information Data Format (PIDF)",
draft-ietf-simple-rpid-07 (work in progress), June 2005.
[14] Peterson, J. and C. Jennings, "Enhancements for Authenticated
Identity Management in the Session Initiation Protocol (SIP)",
draft-ietf-sip-identity-05 (work in progress), May 2005.
[15] Rosenberg, J., "A Data Model for Presence",
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draft-ietf-simple-presence-data-model-02 (work in progress),
February 2005.
[16] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
January 2004.
[17] Peterson, J., "A Privacy Mechanism for the Session Initiation
Protocol (SIP)", RFC 3323, November 2002.
[18] Schulzrinne, H., "The tel URI for Telephone Numbers", RFC 3966,
December 2004.
11.2 Informative References
[19] Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence
and Instant Messaging", RFC 2778, February 2000.
[20] Day, M., Aggarwal, S., Mohr, G., and J. Vincent, "Instant
Messaging / Presence Protocol Requirements", RFC 2779,
February 2000.
[21] Rosenberg, J., "An Extensible Markup Language (XML)
Representation for Expressing Presence Policy Capabilities",
draft-rosenberg-simple-pres-policy-caps-02 (work in progress),
February 2005.
[22] Rosenberg, J., "A Presence Event Package for the Session
Initiation Protocol (SIP)", RFC 3856, August 2004.
[23] Jennings, C., Peterson, J., and M. Watson, "Private Extensions
to the Session Initiation Protocol (SIP) for Asserted Identity
within Trusted Networks", RFC 3325, November 2002.
Author's Address
Jonathan Rosenberg
Cisco Systems
600 Lanidex Plaza
Parsippany, NJ 07054
US
Phone: +1 973 952-5000
Email: jdrosen@cisco.com
URI: http://www.jdrosen.net
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Acknowledgment
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