AuthenticatorResponse: clientDataJSON property

Secure context: This feature is available only in secure contexts (HTTPS), in some or all supporting browsers.

The clientDataJSON property of the AuthenticatorResponse interface stores a JSON string in an ArrayBuffer, representing the client data that was passed to navigator.credentials.create() or navigator.credentials.get(). This property is only accessed on one of the child objects of AuthenticatorResponse, specifically AuthenticatorAttestationResponse or AuthenticatorAssertionResponse.

Value

An ArrayBuffer.

Instance properties

After the clientDataJSON object is converted from an ArrayBuffer to a JavaScript object, it will have the following properties:

challenge

The base64url encoded version of the cryptographic challenge sent from the relying party's server. The original value are passed as the challenge option in CredentialsContainer.get() or CredentialsContainer.create().

crossOrigin Optional

A boolean. If set to true, it means that the calling context is an <iframe> that is not same origin with its ancestor frames.

origin

The fully qualified origin of the relying party which has been given by the client/browser to the authenticator. We should expect the relying party's id to be a suffix of this value.

tokenBinding Optional

An object describing the state of the token binding protocol for the communication with the relying party. It has two properties:

  • status: A string which is either "supported" which indicates the client support token binding but did not negotiate with the relying party or "present" when token binding was used already
  • id: A string which is the base64url encoding of the token binding ID which was used for the communication.

Should this property be absent, it would indicate that the client does not support token binding.

Note: tokenBinding is deprecated as of Level 3 of the spec, but the field is reserved so that it won't be reused for a different purpose.

topOrigin Optional

Contains the fully qualified top-level origin of the relying party. It is set only if it crossOrigin is true.

type

A string which is either "webauthn.get" when an existing credential is retrieved or "webauthn.create" when a new credential is created.

Examples

js
function arrayBufferToStr(buf) {
  return String.fromCharCode.apply(null, new Uint8Array(buf));
}

// pk is a PublicKeyCredential that is the result of a create() or get() Promise
const clientDataStr = arrayBufferToStr(pk.response.clientDataJSON);
const clientDataObj = JSON.parse(clientDataStr);

console.log(clientDataObj.type); // "webauthn.create" or "webauthn.get"
console.log(clientDataObj.challenge); // base64 encoded String containing the original challenge
console.log(clientDataObj.origin); // the window.origin

Specifications

Specification
Web Authentication: An API for accessing Public Key Credentials - Level 3
# dom-authenticatorresponse-clientdatajson

Browser compatibility

BCD tables only load in the browser