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 
Deprecated

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.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
---------------------

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