/** \page page_portal PipeWire Portal access control

This document explains how clients from the portal are handled.

## The portal

The portal is a DBus service that exposes a couple of interfaces to
request access to the PipeWire daemon to perform a certain set of
functions.

The portal makes it possible to use PipeWire without having to expose
the local PipeWire socket in the sandboxed application. PipeWire can
detect and enforce extra permission checks on the Portal session.

Once such portal is the Camera portal that provides a PipeWire session
to stream video from a camera.

In the portal case, it is the portal itself that will make a connection
to the PipeWire daemon to configure the session. It then hands the
file descriptor of the PipeWire connection to the client. The client
can then use the file descriptor to interface with the PipeWire
session.

When the portal connects, it will set the following properties on the
client object:

 * "pipewire.access.portal.is_portal" = true when this connection is the
    portal itself and not a client it is managing.
 * "pipewire.access.portal.app_id" the application id of the client.
 * "pipewire.access.portal.media_roles" media roles of the client.
    Currently "Camera" is defined.

Before returning the connection to a client, the portal will configure
minimal permissions on the client. No objects are initialy visible. It is
the task of the session manager to make the objects in the graph
visible, depending on the client media_roles.

## The PipeWire portal module

\subpage page_module_portal

The pipewire daemon uses the portal module to find the PID of the
processes that owns the DBus name "org.freedesktop.portal.Desktop".

It can then detect clients that connect from this PID and tag them
as PW_KEY_ACCESS "portal". It will also set ALL permissions for this
client so that it can resume. See also \ref page_module_access.


## The client

A client can ask the portal for a connection to the PipeWire daemon.

It receives a file descriptor that can then be used to interface with
the PipeWire daemon.

The connection will have been tagged by the portal as shown above and
will have limited permissions.


## The session manager

The session manager listens for new clients to appear. It will use the
PW_KEY_ACCESS property to find portal connections.

Based on the media_roles it will enable or disable access to PipeWire
objects. It might have to consult a database to decide what is
allowed.

The permission store can be used for this. Usually the portal also
implements "org.freedesktop.impl.portal.PermissionStore" for this.


## Use cases

### new portal managed clients need device permissions configured

When a new client is detected, the available objects are scanned and
permissions are configured for each of them.

Only the devices belonging to the media_roles given by the
portal are considered.

### new devices need to be made visible to portal managed clients

Newly created objects are made visible to a client when the client
is allowed to interact with it.

Only the devices belonging to the media_roles given by the
portal are considered.

### permissions for a device need to be revoked

The session manager listens to changes in the permissions of devices
and will remove the client permissions accordingly.

Usually this is implemented by listening to the permission store
DBus object. The desktop environment might provide a configuration panel
where these permissions can be managed.

## pipewire-media-session

The example media session has an access-portal module that handles the
clients that have a PW_KEY_ACCESS as "portal". Other clients are
ignored.

It currently only handles the camera media_roles and asks the permission
store for camera device permissions. It receives an array of app_id
and the associated permissions. It enables all camera objects when the
camera permissions is given to the app_id of the client.

For new nodes that appear, it will check if the client is allowed to
see them or not and set the permissions on the new object accordingly.

It watches changes in the permission stored and updates the permissions
of the objects of clients accordingly.


*/