To facilitate presence authorization, IBM® WebSphere® Presence Server Component supports watcher information.
Presence Server supports watcher information as defined by IETF RFC 3857 and RFC 3858.
A watcher is defined as an entity that requests information about a resource, or user. These requests are made by means of subscriptions. The watcher information for any given resource is a list of all the subscriptions' status to that resource.
Watcher information consists of the current state for all subscriptions to a particular resource. Monitoring watcher information helps you control access to a resource because it provides the raw data you need to create and deploy presence authorization rules.
Examples of subscription states include active, waiting, pending, and terminated. Subscription state is dynamic, changing as users request new subscriptions, as old subscriptions expire, and as subscriptions are approved or rejected by the resource's owners. As a result, it often useful to subscribe to the watcher information for a particular resource.
The combination of watcher information and presence authorization rules enables the use of reactive authorization, where authorization occurs through direct user intervention. A user can subscribe to the watcher information for his or her presentity and thus find out when a new watcher is added who is not covered by the existing authorization rules. The user may then add a new authorization rule for the new watcher.
Presence Server also has configuration options to control what information is available to watchers, including white and black lists. Refer to the Configuring section of this information center for more information.