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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>
Permissions
</title>
<script src="https://www.w3.org/Tools/respec/respec-w3c" async class="remove"></script>
<script class="remove">
// All config options at https://respec.org/docs/
var respecConfig = {
// Working Groups ids at https://respec.org/w3c/groups/
shortName: "permissions",
group: "webappsec",
specStatus: "ED",
editors: [
{
name: "Marcos Cáceres",
url: "https://marcosc.com",
company: "Apple Inc.",
companyURL: "https://www.apple.com/",
w3cid: "39125",
},
{
name: "Mike Taylor",
url: "https://miketaylr.com/posts/",
companyURL: "https://google.com/",
company: "Google LLC",
w3cid: "90704",
},
],
formerEditors: [
{
name: "Mounir Lamouri",
companyURL: "https://google.com/",
company: "Google LLC",
},
{
name: "Jeffrey Yasskin",
companyURL: "https://google.com/",
company: "Google LLC",
w3cid: "72192",
},
],
github: {
branch: "main",
repoURL: "w3c/permissions",
},
mdn: true,
// See https://respec.org/docs/#xref for usage.
xref: {
profile: "web-platform",
specs: ["permissions-policy", "w3c-process"],
},
caniuse: {
feature: "permissions-api",
removeOnSave: false,
}
};
</script>
</head>
<body>
<h2 id="subtitle">
Interacting with Permissions for Powerful Features
</h2>
<section id="abstract">
<p>
This specification defines common infrastructure that other specifications can use to
interact with browser permissions. These permissions represent a user's choice to allow or
deny access to "powerful features" of the platform. For developers, the specification
standardizes an API to query the permission state of a powerful feature, and be notified if
a permission to use a powerful feature changes state.
</p>
</section>
<section id="sotd">
<p>
This is a work in progress.
</p>
</section>
<section class="informative">
<h2 id="intro">
Introduction
</h2>
<p>
Specifications can define features that are explicitly identified as a [=powerful
feature=]. These features are said to be "powerful" in that they can have significant
privacy, security, and performance implications. As such, users rely on user agents to deny
sites the ability to use these features until they have given express permission, and
usually only granting this ability for a limited amount of time. Express permission to
allow a site to use a powerful feature is generally given and controlled through browser
UI, as illustrated below.
</p>
<figure>
<img src="docs/assets/images/sample-prompts.png" alt=
"On the left, a mockup of a notifications prompt with an allow and don't allow buttons that states 'the website example.com would like to send you notifications'. On the right, a prompt near the URL bar asking to give permission to the camera and microphone to the example site.">
<figcaption>
Sketches of possible permission prompt types
</figcaption>
</figure>
<p>
In this sense, a permission represents the current state of user consent for certain types
of features, and particularly "powerful features". Ultimately the user retains control of
these permissions and have the ability to manually grant or deny permissions through user
preferences. Further, user agents assist users in managing permissions by, for example,
hiding and automatically denying certain permission prompts that would otherwise be a
nuisance, and automatically expiring granted permissions if a user doesn't visit a website
for some time.
</p>
</section>
<figure>
<img src="docs/assets/images/permission-settings.png" alt=
"A mockup of a settings page that would allow a user to set or reset defaults for location, camera, microphone, motion sensors, and notifications permissions.">
<figcaption>
A sketch of a possible site-specific permissions controls UI
</figcaption>
</figure>
<section class="informative">
<h2 id="examples">
Examples of usage
</h2>
<p>
This example uses the Permissions API to decide whether local news should be shown using
the Geolocation API or with a button offering to add the feature.
</p>
<pre class="example js" title="Using .state attribute">
const { state } = await navigator.permissions.query({
name: "geolocation"
});
switch (state) {
case "granted":
showLocalNewsWithGeolocation();
break;
case "prompt":
showButtonToEnableLocalNews();
break;
case "denied":
showNationalNews();
break;
}
</pre>
<p>
This example simultaneously checks the state of the `"geolocation"` and `"notifications"`
[=powerful features=]:
</p>
<pre class="example js" title="Checking the state of multiple permissions">
const queryPromises = ["geolocation", "notifications"].map(
name => navigator.permissions.query({ name })
);
for await (const status of queryPromises) {
console.log(`${status.name}: ${status.state}`);
}
</pre>
<p>
This example is checking the permission state of the available cameras.
</p>
<pre class="example js" title="Checking permission state of multiple cameras">
const devices = await navigator.mediaDevices.enumerateDevices();
// filter on video inputs, and map to query object
const queries = devices
.filter(({ kind }) => kind === "videoinput")
.map(({ deviceId }) => ({ name: "camera", deviceId }));
const promises = queries.map((queryObj) =>
navigator.permissions.query(queryObj)
);
try {
const results = await Promise.all(promises);
// log the state of each camera
results.forEach(({ state }, i) => console.log("Camera", i, state));
} catch (error) {
console.error(error);
}
</pre>
</section>
<section>
<h2>
Model
</h2>
<p>
This section specifies a model for [=permissions=] to use [=powerful features=] on the Web
platform.
</p>
<section>
<h3>
Permissions
</h3>
<p>
A <dfn class="export">permission</dfn> represents a user's decision to allow a web
application to use a [=powerful feature=]. This decision is represented as a permission
[=permission/state=].
</p>
<p>
<dfn class="export">Express permission</dfn> refers to the user
[=permission/grants|granting=] the web application the ability to use a [=powerful
feature=].
</p>
<aside class="note" title="Limitations and extensibility">
<p>
Current Web APIs have different ways to deal with permissions. For example, the
[[[notifications]]] allows developers to request a permission and check the permission
status explicitly. Others expose the status to web pages only when they try to use the
API, e.g., the [[[Geolocation]]] which fails if the permission was not granted without
allowing the developer to check beforehand.
</p>
<p>
The solution described in this document is meant to be extensible, but isn't expected
to be applicable to all the current and future permissions available in the web
platform. Working Groups that are creating specifications whose permission model
doesn't fit in the model described in this document should contact the editors by
<a href="https://github.com/w3c/permissions/issues">filing an issue</a>.
</p>
</aside>
<p>
Conceptually, a [=permission=] for a [=powerful feature=] can be in one of the following
<dfn data-dfn-for="permission" data-local-lt="state">states</dfn>:
</p>
<dl data-sort="">
<dt>
<dfn class="export" data-lt="prompt" data-dfn-for="permission">"prompt"</dfn>:
</dt>
<dd>
The user has not given [=express permission=] to use the feature (i.e., it's the same
as [=permission/"denied"=]). It also means that if a caller attempts to use the
feature, the [=user agent=] will either be prompting the user for permission or access
to the feature will be [=permission/"denied"=].
</dd>
<dt>
<dfn class="export" data-lt="granted" data-local-lt="grant" data-dfn-for=
"permission">"granted"</dfn>:
</dt>
<dd>
The user, or the user agent on the user's behalf, has given [=express permission=] to
use a [=powerful feature=]. The caller will be able to use the feature possibly without
having the [=user agent=] asking the user's permission.
</dd>
<dt>
<dfn class="export" data-lt="denied" data-dfn-for="permission">"denied"</dfn>:
</dt>
<dd>
The user, or the user agent on the user's behalf, has denied access to this [=powerful
feature=]. The caller won't be able to use the feature.
</dd>
</dl>
<p>
To ascertain <dfn class="export">new information about the user's intent</dfn>, a user
agent MAY collect and interpret information about a user's intentions. This information
can come from explicit user action, aggregate behavior of both the relevant user and
other users, or <dfn>implicit signals</dfn> this specification hasn't anticipated.
</p>
<aside class="note" data-cite="appmanifest" title="What constitutes an implicit signal?">
<p>
The [=implicit signals=] could be, for example, the [=installed web
application|installation=] status of a web application or frequency and recency of
visits. A user that has installed a web application and used it frequently and recently
is more likely to trust it. Implementations are advised to exercise caution when
relying on implicit signals.
</p>
</aside>
<p data-cite="ECMAScript">
Every [=permission=] has a <dfn class="export" data-dfn-for="permission">lifetime</dfn>,
which is the duration for which a particular permission remains [=permission/"granted"=]
before it reverts back to its [=permission/default state=]. A [=permission/lifetime=]
could be until a particular [=ECMAScript/Realm=] is destroyed, until a particular
[=top-level browsing context=] is destroyed, a particular amount of time, or be infinite.
The lifetime is negotiated between the end-user and the [=user agent=] when the user
gives [=express permission=] to use a [=feature=]—usually via some permission UI or
user-agent defined policy.
</p>
<p>
Every permission has a <dfn data-for="permission">default state</dfn> (usually
[=permission/"prompt"=]), which is the [=permission/state=] that the permission is in
when the user has not yet given [=express permission=] to use the [=feature=] or it has
been reset because its [=permission/lifetime=] has expired.
</p>
</section>
<section>
<h3>
Permission Store
</h3>
<p>
The user agent maintains a single <dfn class="export">permission store</dfn> which is a
[=/list=] of [=permission store entries=]. Each particular [=entry=] denoted by its
[=permission store entry/descriptor=] and [=permission store entry/key=] can only appear
at most once in this list.
</p>
<p>
The user agent MAY remove [=entries=] from the [=permission store=] when their respective
[=permission=]'s [=permission/lifetime=] has expired.
</p>
<p>
A <dfn class="export" data-local-lt="entry">permission store entry</dfn> is a [=tuple=]
of {{PermissionDescriptor}} <dfn class="export" data-dfn-for=
"permission store entry">descriptor</dfn>, [=permission key=] <dfn class="export"
data-dfn-for="permission store entry">key</dfn>, and [=permission/state=] <dfn class=
"export" data-dfn-for="permission store entry">state</dfn>.
</p>
<div class="algorithm">
<p>
To <dfn class="export">get a permission store entry</dfn> given a
{{PermissionDescriptor}} |descriptor:PermissionDescriptor| and [=permission key=]
|key|:
</p>
<ol>
<li>
<!-- TODO: PermissionDescriptor equality is not defined (#396) -->
If the user agent's [=permission store=] [=list/contains=] an [=entry=] whose
[=permission store entry/descriptor=] is |descriptor|, and whose [=permission store
entry/key=] [=permission key/is equal to=] |key| given |descriptor|, return that
entry.
</li>
<li>Return null.
</li>
</ol>
</div>
<div class="algorithm">
<p>
To <dfn class="export">set a permission store entry</dfn> given a
{{PermissionDescriptor}} |descriptor:PermissionDescriptor|, a [=permission key=] |key|,
and a [=permission/state=] |state|, run these steps:
</p>
<ol>
<li>Let |newEntry| be a new [=permission store entry=] whose [=permission store
entry/descriptor=] is |descriptor|, and whose [=permission store entry/key=] is |key|,
and whose [=permission store entry/state=] is |state|.
</li>
<li>If the user agent's [=permission store=] [=list/contains=] an [=entry=] whose
[=permission store entry/descriptor=] is |descriptor|, and whose [=permission store
entry/key=] [=permission key/is equal to=] |key| given |descriptor|, [=list/replace=]
that entry with |newEntry| and abort these steps.
</li>
<li>[=list/Append=] |newEntry| to the user agent's [=permission store=].
</li>
</ol>
</div>
<div class="algorithm">
<p>
To <dfn class="export">remove a permission store entry</dfn> given a
{{PermissionDescriptor}} |descriptor:PermissionDescriptor| and [=permission key=]
|key|, run these steps:
</p>
<ol>
<li>[=list/Remove=] the [=entry=] whose [=permission store entry/descriptor=] is
|descriptor|, and whose [=permission store entry/key=] [=permission key/is equal to=]
|key| given |descriptor|, from the user agent's [=permission store=].
</li>
</ol>
</div>
<p>
A <dfn class="export">permission key</dfn> has its type defined by a feature's [=powerful
feature/permission key type=].
</p>
<aside class="note">
The permission key defines the scope of a permission grant, which is usually per-origin.
Powerful features may override the [=powerful feature/permission key type=] to specify a
custom permission key. This is useful for features that want to change the granularity of
permissions based on additional context, such as double-keying on both an embedded origin
and a top-level origin.
</aside>
<div class="algorithm">
<p>
To determine whether a [=permission key=] |key1| <dfn class="export" data-dfn-for=
"permission key">is equal to</dfn> a [=permission key=] |key2|, given a
{{PermissionDescriptor}} |descriptor|, run the following steps:
</p>
<ol>
<li>If |key1| is not of |descriptor|'s [=powerful feature/permission key type=] or
|key2| is not of |descriptor|'s [=powerful feature/permission key type=], return false.
</li>
<li>Return the result of running the [=powerful feature/permission key comparison
algorithm=] for the feature named by |descriptor|'s {{PermissionDescriptor/name}},
passing |key1| and |key2|.
</li>
</ol>
</div>
</section>
<section>
<h2>
Powerful features
</h2>
<p data-cite="permissions-policy">
A <dfn class="export" data-local-lt="feature">powerful feature</dfn> is a web platform
feature (usually an API) for which a user gives [=express permission=] before the feature
can be used. Except for a few notable exceptions (e.g., the [[[Notifications]]]), most
powerful features are also [=policy-controlled features=]. For powerful features that are
also [=policy-controlled features=], [[Permissions-Policy]] controls whether a
[=document=] is [=allowed to use=] a given feature. That is, a powerful feature can only
request [=express permission=] from a user if the [=document=] has permission delegated
to it via the corresponding [=policy-controlled feature=] (see example below). Subsequent
access to the feature is determined by the user having [=permission/"granted"=]
permission, or by satisfying some criteria that is equivalent to a permission
[=permission/grant=].
</p>
<aside class="example" title="Powerful features are policy-controlled features">
<p>
This example shows how the permissions policy set through the [^iframe/allow^]
attribute controls whether the [^iframe^] is [=allowed to use=] a powerful feature.
Because `"geolocation"` is allowed, the [^iframe^]'s document can request permission
from the user to use the [[[Geolocation]]] (i.e., it will prompt the user for express
permission to access their location information). However, requesting permission to use
any other feature will be automatically denied, because they are not listed in the
[^iframe/allow^] attribute.
</p>
<pre class="html">
<iframe src="https://example.com/" allow="geolocation">
</iframe>
</pre>
<p>
See [[[#relationship-to-permissions-policy]]] for more information.
</p>
</aside>
<p>
A [=powerful feature=] is identified by its <dfn class="export" data-dfn-for=
"powerful feature">name</dfn>, which is a string literal (e.g., "geolocation").
</p>
<p>
The user agent tracks which [=powerful features=] the user has [=permission=] to use via
the [=environment settings object=].
</p>
<section>
<h3>
Aspects
</h3>
<p>
Each [=powerful feature=] can define zero or more additional <dfn data-dfn-for=
"powerful feature">aspects</dfn>. An aspect is defined as WebIDL [=dictionary=] that
[=dictionary/inherits=] from {{PermissionDescriptor}} and serves as a WebIDL
interface's [=powerful feature/permission descriptor type=].
</p>
<aside class="example" title="Defining your own permission descriptor type">
<p>
A hypothetical [=powerful feature=] "food detector API" has two [=powerful
feature/aspects=] that allow sensing taste and smell. So, a specification would
define a new WebIDL interface that [=dictionary/inherits=] {{PermissionDescriptor}}:
</p>
<pre>
dictionary SensesPermissionDescriptor : PermissionDescriptor {
boolean canSmell = false;
boolean canTaste = false;
};
</pre>
<p>
Which would then be queried via the API in the following way:
</p>
<pre class="js">
// Check if the "senses" powerful feature is allowed to smell things
const status = await navigator.permissions.query({
name: "senses",
canSmell: true,
});
// Do something interesting with the status.
</pre>
<p>
A user can restrict the "senses" powerful feature to only "taste", in which case the
{{PermissionStatus}}'s {{PermissionStatus/state}} above would be
{{PermissionState/"denied"}} .
</p>
</aside>
</section>
</section>
<section>
<h3>
Permissions task source
</h3>
<p>
The <dfn>permissions task source</dfn> is a [=task source=] used to perform
permissions-related [=tasks=] in this specification.
</p>
</section>
</section>
<section>
<h2>
Specifying a powerful feature
</h2>
<p>
When a conforming [=specification=] <dfn class="export">specifies a powerful feature</dfn>
it:
</p>
<ol>
<li>MUST give the [=powerful feature=] a [=powerful feature/name=] in the form of a [=ascii
lowercase=] string.
</li>
<li>MAY define a [=powerful feature/permission descriptor type=] that inherits from
{{PermissionDescriptor}}.
</li>
<li>MAY define zero or more [=powerful feature/aspects=].
</li>
<li>MAY override the algorithms and types given below if the defaults are not suitable for
a particular [=powerful feature=].
</li>
<li>MUST register the [=powerful feature=] in the [[[permissions-registry]]].
</li>
</ol>
<p class="advisement">
Registering the newly specified [=powerful features=] in the [[[permissions-registry]]]
gives this Working Group an opportunity to provide feedback and check that integration with
this specification is done effectively.
</p>
<dl>
<dt>
A <dfn data-dfn-for="powerful feature" class="export">permission descriptor type</dfn>:
</dt>
<dd>
<p>
{{PermissionDescriptor}} or one of its subtypes. If unspecified, this defaults to
{{PermissionDescriptor}}.
</p>
<p>
The feature can define a <a href=
"https://en.wikipedia.org/wiki/Partially_ordered_set">partial order</a> on descriptor
instances. If |descriptorA| is <dfn class="export" data-dfn-for=
"PermissionDescriptor">stronger than</dfn> |descriptorB|, then if |descriptorA|'s
[=permission state=] is {{PermissionState/"granted"}}, |descriptorB|'s [=permission
state=] must also be {{PermissionState/"granted"}}, and if |descriptorB|'s [=permission
state=] is {{PermissionState/"denied"}}, |descriptorA|'s [=permission state=] must also
be {{PermissionState/"denied"}}.
</p>
<aside class="example" id="example-stronger-than" title=
"A permission descriptor that defines a partial order">
<p>
<code>{name: "midi", sysex: true}</code> ("midi-with-sysex") is
[=PermissionDescriptor/stronger than=] <code>{name: "midi", sysex: false}</code>
("midi-without-sysex"), so if the user denies access to midi-without-sysex, the UA
must also deny access to midi-with-sysex, and similarly if the user grants access to
midi-with-sysex, the user agent must also grant access to midi-without-sysex.
</p>
</aside>
</dd>
<dt>
<dfn data-dfn-for="powerful feature" class="export">permission state constraints</dfn>:
</dt>
<dd>
Constraints on the values that the user agent can return as a descriptor's [=permission
state=]. Defaults to no constraints beyond the user's intent.
</dd>
<dt>
<dfn data-dfn-for="powerful feature" class="export">extra permission data type</dfn>:
</dt>
<dd>
<p>
Some [=powerful features=] have more information associated with them than just a
{{PermissionState}}. Each of these features defines an [=powerful feature/extra
permission data type=].
</p>
<p class="note" data-cite="mediacapture-streams ECMAScript">
For example, {{MediaDevices/getUserMedia()}} needs to determine <em>which</em> cameras
the user has granted permission to access.
</p>
<div class="algorithm">
<p>
If a {{DOMString}} |name| names one of these features, then |name|'s
<dfn data-dfn-for="powerful feature" class="export">extra permission data</dfn> for
an optional <a>environment settings object</a> |settings| is the result of the
following algorithm:
</p>
<ol>
<li>If |settings| wasn't passed, set it to the [=current settings object=].
</li>
<li>If there was a previous invocation of this algorithm with the same |name| and
|settings|, returning |previousResult|, and the user agent has not received <a>new
information about the user's intent</a> since that invocation, return
|previousResult|.
</li>
<li>Return the instance of |name|'s [=powerful feature/extra permission data type=]
that matches the UA's impression of the user's intent, taking into account any
[=powerful feature/extra permission data constraints=] for |name|.
</li>
</ol>
</div>
<p>
If specified, the [=powerful feature/extra permission data=] algorithm is usable for
this feature.
</p>
</dd>
<dt>
Optional <dfn data-dfn-for="powerful feature" class="export">extra permission data
constraints</dfn>:
</dt>
<dd>
Constraints on the values that the user agent can return as a [=powerful feature=]'s
[=powerful feature/extra permission data=]. Defaults to no constraints beyond the user's
intent.
</dd>
<dt>
A <dfn data-dfn-for="powerful feature" class="export">permission result type</dfn>:
</dt>
<dd>
{{PermissionStatus}} or one of its subtypes. If unspecified, this defaults to
{{PermissionStatus}}.
</dd>
<dt>
A <dfn data-dfn-for="powerful feature" class="export">permission query algorithm</dfn>:
</dt>
<dd>
<p>
Takes an instance of the [=powerful feature/permission descriptor type=] and a new or
existing instance of the [=powerful feature/permission result type=], and updates the
[=powerful feature/permission result type=] instance with the query result. Used by
{{Permissions}}' {{Permissions/query(permissionDesc)}} method and the
[=`PermissionStatus` update steps=]. If unspecified, this defaults to the [=default
permission query algorithm=].
</p>
<div class="algorithm">
<p>
The <dfn data-export="">default permission query algorithm</dfn>, given a
{{PermissionDescriptor}} <var>permissionDesc</var> and a {{PermissionStatus}}
|status|, runs the following steps:
</p>
<ol>
<li>Set <code>|status|</code>'s {{PermissionStatus/state}} to |permissionDesc|'s <a>
permission state</a>.
</li>
</ol>
</div>
</dd>
<dt>
A <dfn data-dfn-for="powerful feature" class="export">permission key type</dfn>:
</dt>
<dd>
<p>
The type of [=permission key=] used by the feature. Defaults to [=origin=]. A feature
that specifies a custom [=powerful feature/permission key type=] MUST also specify a
[=powerful feature/permission key generation algorithm=].
</p>
</dd>
<dt>
A <dfn data-dfn-for="powerful feature" class="export">permission key generation
algorithm</dfn>:
</dt>
<dd>
<p>
Takes an [=origin=] |origin| and an [=origin=] |embedded origin|, and returns a new
[=permission key=]. If unspecified, this defaults to the [=default permission key
generation algorithm=]. A feature that specifies a custom [=powerful feature/permission
key generation algorithm=] MUST also specify a [=powerful feature/permission key
comparison algorithm=].
</p>
<div class="algorithm">
<p>
The <dfn class="export">default permission key generation algorithm</dfn>, given an
[=origin=] |origin| and an [=origin=] |embedded origin|, runs the following steps:
</p>
<ol>
<li>Return |origin|.
</li>
</ol>
</div>
<aside class="note" title="Permission Delegation">
Most powerful features grant permission to the top-level origin and delegate access to
the requesting document via [[[Permissions-Policy]]]. This is known as permission
delegation.
</aside>
</dd>
<dt>
A <dfn data-dfn-for="powerful feature" class="export">permission key comparison
algorithm</dfn>:
</dt>
<dd>
<p>
Takes two [=permission keys=] and returns a [=boolean=] that shows whether the two keys
are equal. If unspecified, this defaults to the [=default permission key comparison
algorithm=].
</p>
<div class="algorithm">
<p>
The <dfn class="export">default permission key comparison algorithm</dfn>, given
[=permission keys=] |key1| and |key2|, runs the following steps:
</p>
<ol>
<li>Return |key1| is [=same origin=] with |key2|.
</li>
</ol>
</div>
</dd>
<dt>
A <dfn data-dfn-for="powerful feature" class="export">permission revocation
algorithm</dfn>:
</dt>
<dd>
<p>
Takes no arguments. Updates any other parts of the implementation that need to be kept
in sync with changes in the results of [=permission states=] or [=powerful
feature/extra permission data=].
</p>
<p>
If unspecified, this defaults to running [=react to the user revoking permission=].
</p>
</dd>
<dt>
A permission [=permission/lifetime=]:
</dt>
<dd>
<p>
Specifications that define one or more [=powerful features=] SHOULD suggest a
[=permission=] [=permission/lifetime=] that is best suited for the particular feature.
Some guidance on determining the lifetime of a permission is noted below, with a strong
emphasis on user privacy. If no [=permission/lifetime=] is specified, the user agent
provides one.
</p>
<p>
When the permission [=permission/lifetime=] expires for an origin:
</p>
<ol>
<li>Set the permission back to its default [=permission state=] (e.g., by setting it
back to [=permission/"prompt"=]).
</li>
<li>For each |browsing context| associated with the origin (if any), [=queue a global
task=] on the [=permissions task source=] with the |browsing context|'s [=global
object=] to run the [=powerful feature/permission revocation algorithm=].
</li>
</ol>
<aside class="note" title="Determining the lifetime of a permission">
<p>
For particularly privacy-sensitive [=features=], such as [[[GETUSERMEDIA]]], which
can provide a web application access to a user's camera and microphone, some user
agents expire a permission [=permission/grant=] as soon as a browser tab is closed or
[=navigated=]. For other features, like the [[[Geolocation]]], user agents are known
to offer a choice of only granting the permission for the session, or for one day.
Others, like the [[[Notifications]]] and [[[push-api]]] APIs, remember a user's
decision indefinitely or until the user manually revokes the permission. Note that
permission [=permission/lifetimes=] can vary significantly between user agents.
</p>
<p>
Finding the right balance for the lifetime of a permission requires a lot of thought
and experimentation, and often evolves over a period of years. Implementers are
encouraged to work with their UX security teams to find the right balance between
ease of access to a [=powerful feature=] (i.e., reducing the number of permission
prompts), respecting a user's privacy, and making users aware when a web application
is making use of a particular powerful feature (e.g., via some visual or auditory UI
indicator).
</p>
<p>
If you are unsure about what [=permission/lifetime=] to suggest for a [=powerful
feature=], please contact the <a href="https://www.w3.org/Privacy/IG/">Privacy
Interest Group</a> for guidance.
</p>
</aside>
</dd>
<dt>
<dfn class="export" data-dfn-for="powerful feature">Default permission state</dfn>:
</dt>
<dd>
<p>
An {{PermissionState}} value that serves as a [=permission=]'s [=permission/default
state=] of a [=powerful feature=].
</p>
<p>
If not specified, the [=permission=]'s [=permission/default state=] is
{{PermissionState/"prompt"}}.
</p>
</dd>
</dl>
<p>
A <dfn class="export">default powerful feature</dfn> is a [=powerful feature=] with all of
the above types and algorithms defaulted.
</p>
</section>
<section>
<h2>
Algorithms to interface with permissions
</h2>
<section data-cite="permissions-policy">
<h3 id="reading-current-states">
Reading the current permission state
</h3>
<div class="algorithm">
<p>
To <dfn class="export" data-lt="getting the current permission state">get the current
permission state</dfn>, given a [=powerful feature/name=] |name| and an optional
[=environment settings object=] |settings|, run the following steps. This algorithm
returns a {{PermissionState}} enum value.
</p>
<ol>
<li>Let |descriptor:PermissionDescriptor| be a newly-created {{PermissionDescriptor}}
with {{PermissionDescriptor/name}} initialized to |name|.
</li>
<li>Return the [=permission state=] of |descriptor| with |settings|.
</li>
</ol>
</div>
<div class="algorithm">
<p>
A |descriptor|'s <dfn class="export">permission state</dfn>, given an optional
<a>environment settings object</a> |settings| is the result of the following algorithm.
It returns a {{PermissionState}} enum value:
</p>
<ol>
<li>If |settings| wasn't passed, set it to the [=current settings object=].
</li>
<li>If |settings| is a [=non-secure context=], return {{PermissionState/"denied"}}.
</li>
<li>Let |feature| be |descriptor|'s {{PermissionDescriptor/name}}.
</li>
<li class="algorithm">If there exists a [=policy-controlled feature=] for |feature| and
|settings|' [=relevant global object=] has an [=associated `Document`=] run the
following step:
<ol>
<li>Let <var>document</var> be |settings|' [=relevant global object=]'s
[=associated `Document`=].
</li>
<li>If <var>document</var> is not <a>allowed to use</a> |feature|, return
{{PermissionState/"denied"}}.
</li>
</ol>
</li>
<li>Let |key| be the result of [=powerful feature/permission key generation
algorithm|generating a permission key=] for |descriptor| with |settings|'s
[=environment/top-level origin=] and |settings|'s [=environment settings
object/origin=].
</li>
<li>Let |entry| be the result of [=get a permission store entry|getting a permission
store entry=] with |descriptor| and |key|.
</li>
<li>If |entry| is not null, return a {{PermissionState}} enum value from |entry|'s
[=permission store entry/state=].
</li>
<li>Return the {{PermissionState}} enum value that represents the permission state of
|feature|, taking into account any [=powerful feature/permission state constraints=]
for |descriptor|'s {{PermissionDescriptor/name}}.
</li>
</ol>
</div>
<p>
As a shorthand, a {{DOMString}} |name|'s [=permission state=] is the [=permission state=]
of a {{PermissionDescriptor}} with its {{PermissionDescriptor/name}} member set to
|name|.
</p>
</section>
<section>
<h3 id="requesting-more-permission">
Requesting permission to use a powerful feature
</h3>
<div class="algorithm">
<p>
To <dfn data-lt="request permission to use|requesting permission to use" class=
"export">request permission to use</dfn> a |descriptor:PermissionDescriptor|, the user
agent must perform the following steps. This algorithm returns either
{{PermissionState/"granted"}} or {{PermissionState/"denied"}}.
</p>
<ol>
<li>Let <var>current state</var> be the |descriptor|'s <a>permission state</a>.
</li>
<li>If <var>current state</var> is not {{PermissionState/"prompt"}}, return
<var>current state</var> and abort these steps.
</li>
<li>Ask the user for <a>express permission</a> for the calling algorithm to use the <a>
powerful feature</a> described by |descriptor|.
</li>
<li>If the user gives [=express permission=] to use the powerful feature, set |current
state| to {{PermissionState/"granted"}}; otherwise to {{PermissionState/"denied"}}. The
user's interaction may provide <a>new information about the user's intent</a> for the
[=origin=].
<p class="note">
This is intentionally vague about the details of the permission UI and how the user
agent infers user intent. User agents should be able to explore lots of UI within
this framework.
</p>
</li>
<li>Let |settings| be the [=current settings object=].
</li>
<li>Let |key| be the result of [=powerful feature/permission key generation
algorithm|generating a permission key=] for |descriptor| with |settings|'s
[=environment/top-level origin=] and |settings|'s [=environment settings
object/origin=].
</li>
<li>[=Queue a task=] on the [=current settings object=]'s [=environment settings
object/responsible event loop=] to [=set a permission store entry=] with |descriptor|,
|key|, and |current state|.
</li>
<li>Return |current state|.
</li>
</ol>
</div>
<p>
As a shorthand, [=requesting permission to use=] a {{DOMString}} |name|, is the same as
[=requesting permission to use=] a {{PermissionDescriptor}} with its
{{PermissionDescriptor/name}} member set to |name|.
</p>
</section>
<section>
<h3>
Prompt the user to choose
</h3>
<div class="algorithm">
<p>
To <dfn data-lt="prompt the user to choose|prompting the user to choose" class=
"export">prompt the user to choose</dfn> one or more |options| associated with a given
|descriptor:PermissionDescriptor| and an optional <a>boolean</a>
|allowMultiple:boolean| (default false), the user agent must perform the following
steps. This algorithm returns either {{PermissionState/"denied"}} or the user's
selection.
</p>
<ol>
<li>If |descriptor|'s <a>permission state</a> is {{PermissionState/"denied"}}, return
{{PermissionState/"denied"}} and abort these steps.
</li>
<li>If |descriptor|'s <a>permission state</a> is {{PermissionState/"granted"}}, the
user agent may return one (or more if |allowMultiple| is true) of |options| chosen by
the user and abort these steps. If the user agent returns without prompting, then
subsequent <a data-lt="prompt the user to choose">prompts for the user to choose</a>
from the same set of options with the same |descriptor| must return the same option(s),
unless the user agent receives <a>new information about the user's intent</a>.
</li>
<li>Ask the user to choose one or more |options| or deny permission, and wait for them
to choose:
<ol>
<li>If the calling algorithm specified extra information to include in the prompt,
include it.
</li>
<li>If |allowMultiple| is false, restrict selection to a single item from
|options|; otherwise, any number may be selected by the user.
</li>
</ol>
</li>
<li>If the user chose one or more options, return them; otherwise return
{{PermissionState/"denied"}}.
<p class="note">
This is intentionally vague about the details of the permission UI and how the user
agent infers user intent. User agents should be able to explore lots of UI within
this framework (e.g., a permission prompt could time out and automatically return
"denied" without the user making an explicit selection).
</p>
</li>
</ol>
</div>
<p>
As a shorthand, [=prompting the user to choose=] from options associated with a
{{DOMString}} |name|, is the same as [=prompting the user to choose=] from those options
associated with a {{PermissionDescriptor}} with its {{PermissionDescriptor/name}} member
set to |name|.
</p>
</section>
<section>
<h3 id="reacting-to-revocation">
Reacting to users revoking permission
</h3>
<div class="algorithm">
<p>
When the user agent learns that the user no longer intends to grant permission to use a
feature described by the {{PermissionDescriptor}} |descriptor| in the context described
by the [=permission key=] |key|, <dfn>react to the user revoking permission</dfn> by
running these steps:
</p>
<ol>
<li>Run |descriptor|'s {{PermissionDescriptor/name}}'s [=powerful feature/permission
revocation algorithm=].
</li>
<li>[=Remove a permission store entry=] with |descriptor| and |key|.
</li>
</ol>
</div>
</section>
</section>
<section>
<h2>
Permissions API
</h2>
<section>
<h3 id="navigator-and-workernavigator-extension">
Extensions to the `Navigator` and `WorkerNavigator` interfaces
</h3>
<pre class="idl">
[Exposed=(Window)]
partial interface Navigator {
[SameObject] readonly attribute Permissions permissions;
};
[Exposed=(Worker)]
partial interface WorkerNavigator {
[SameObject] readonly attribute Permissions permissions;
};
</pre>
</section>
<section data-dfn-for="Permissions">
<h3 id="permissions-interface">
`Permissions` interface
</h3>
<pre class="idl">
[Exposed=(Window,Worker)]
interface Permissions {
Promise<PermissionStatus> query(object permissionDesc);
};
dictionary PermissionDescriptor {
required DOMString name;
};
</pre>
<section>
<h4 id="query-method">
`query()` method
</h4>
<div class="algorithm">
<p>
When the <dfn>query()</dfn> method is invoked, the <a>user agent</a> MUST run the
following <dfn class="export">query a permission</dfn> algorithm, passing the
parameter <var>permissionDesc</var>:
</p>
<ol>
<li>If [=this=]'s [=relevant global object=] is a {{Window}} object, then: