HTTP Header Series: Feature-Policy

Wednesday, January 29, 2020

Layer One - Director of Digital Delivery - Jim Schram

In our opening to this series, we discussed some of the reasons for Security Headers. In this post we will describe in more detail the (currently experimental) Feature-Policy header which provides a mechanism to allow and deny the use of browser features in its own frame, and in content within any <iframe> elements in the document. This header is similar to the CSP Header but it controls features like access to your camera or microphone.

Feature-Policy Syntax:

Feature-Policy: <policy-directive>; <policy-directive>

where <policy-directive> consists of: <directive> <allowlist> with no internal punctuation.

Feature-Policy Allowlist:

An allowlist is a list of origins that takes one or more of the following values, separated by spaces:

*: The feature will be allowed in this document, and all nested browsing contexts (iframes) regardless of their origin.
'self': The feature will be allowed in this document, and in all nested browsing contexts (iframes) in the same origin.
'src': (In an iframe allow attribute only) The feature will be allowed in this iframe, as long as the document loaded into it comes from the same origin as the URL in the iframe's src attribute.
'none': The feature is disabled in top-level and nested browsing contexts.
<origin(s)>: The feature is allowed for specific origins (for example, https://example.com). Origins should be separated by a space.

The values * (enable for all origins) or 'none' (disable for all origins) may only be used alone, while 'self' and 'src' may be used with one or more origins.

Feature-Policy Directives:

Directive	Description
accelerometer	Controls whether the current document is allowed to gather information about the acceleration of the device through the Accelerometer interface.
ambient-light-sensor	Controls whether the current document is allowed to gather information about the amount of light in the environment around the device through the AmbientLightSensor interface.
autoplay	Controls whether the current document is allowed to autoplay media requested through the HTMLMediaElement interface. When this policy is disabled and there were no user gestures, the Promise returned by HTMLMediaElement.play() will reject with a DOMException. The autoplay attribute on <audio> and <video> elements will be ignored.
battery	Controls whether the use of the Battery Status API is allowed. When this policy is disabled, the Promise returned by Navigator.getBattery() will reject with a NotAllowedError DOMException.
camera	Controls whether the current document is allowed to use video input devices. When this policy is disabled, the Promise returned by getUserMedia() will reject with a NotAllowedError DOMException.
display-capture	Controls whether or not the current document is permitted to use the getDisplayMedia() method to capture screen contents. When this policy is disabled, the promise returned by getDisplayMedia() will reject with a NotAllowedError if permission is not obtained to capture the display's contents.
document-domain	Controls whether the current document is allowed to set document.domain. When this policy is disabled, attempting to set document.domain will fail and cause a SecurityError DOMException to be thrown.
encrypted-media	Controls whether the current document is allowed to use the Encrypted Media Extensions API (EME). When this policy is disabled, the Promise returned by Navigator.requestMediaKeySystemAccess() will reject with a DOMException.
execution-while-not-rendered	Controls whether tasks should execute in frames while they're not being rendered (e.g. if an iframe is hidden or display: none).
execution-while-out-of-viewport	Controls whether tasks should execute in frames while they're outside of the visible viewport.
fullscreen	Controls whether the current document is allowed to use Element.requestFullScreen(). When this policy is disabled, the returned Promise rejects with a TypeError.
geolocation	Controls whether the current document is allowed to use the Geolocation Interface. When this policy is disabled, calls to getCurrentPosition() and watchPosition() will cause those functions' callbacks to be invoked with a PositionError code of PERMISSION_DENIED.
gyroscope	Controls whether the current document is allowed to gather information about the orientation of the device through the Gyroscope interface.
layout-animations	Controls whether the current document is allowed to show layout animations.
legacy-image-formats	Controls whether the current document is allowed to display images in legacy formats.
magnetometer	Controls whether the current document is allowed to gather information about the orientation of the device through the Magnetometer interface.
microphone	Controls whether the current document is allowed to use audio input devices. When this policy is disabled, the Promise returned by MediaDevices.getUserMedia() will reject with a NotAllowedError.
midi	Controls whether the current document is allowed to use the Web MIDI API. When this policy is disabled, the Promise returned by Navigator.requestMIDIAccess() will reject with a DOMException
navigation-override	Controls the availability of mechanisms that enables the page author to take control over the behavior of spatial navigation, or to cancel it outright.
oversized-images	Controls whether the current document is allowed to download and display large images.
payment	Controls whether the current document is allowed to use the Payment Request API. When this policy is enabled, the PaymentRequest() constructor will throw a SecurityError DOMException.
picture-in-picture	Controls whether the current document is allowed to play a video in a Picture-in-Picture mode via the corresponding API.
publickey-credentials-get	Controls whether the current document is allowed to use the Web Authentication API to retreive already stored public-key credentials, i.e. via navigator.credentials.get({publicKey: ..., ...}).
sync-xhr	Controls whether the current document is allowed to make synchronous XMLHttpRequest requests.
usb	Controls whether the current document is allowed to use the WebUSB API.
vr	Controls whether the current document is allowed to use the WebVR API. When this policy is disabled, the Promise returned by Navigator.getVRDisplays() will reject with a DOMException. Keep in mind that the WebVR standard is in the process of being replaced with WebXR.
wake-lock	Controls whether the current document is allowed to use Wake Lock API to indicate that device should not enter power-saving mode.
screen-wake-lock	Controls whether the current document is allowed to use Screen Wake Lock API to indicate that device should not turn off or dim the screen.
web-share	Controls whether or not the current document is allowed to use the Navigator.share() of Web Share API to share text, links, images, and other content to arbitrary destinations of user's choice, e.g. mobile apps.
xr-spatial-tracking	Controls whether or not the current document is allowed to use the WebXR Device API to interact with a WebXR session.

(Source: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Feature-Policy)

Examples:

Feature-Policy: microphone 'none'; geolocation 'none'

Feature-Policy: camera 'self'; fullscreen *

Feature-Policy: camera 'self’ https://example.com; autoplay 'self’ https://example.com

Interested in learning more?