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

The authenticatorData property of the AuthenticatorAssertionResponse interface returns an ArrayBuffer containing information from the authenticator such as the Relying Party ID Hash (rpIdHash), a signature counter, test of user presence, user verification flags, and any extensions processed by the authenticator.


var authnrData = authenticatorAssertionResponse.authenticatorData;


An ArrayBuffer that has a ArrayBuffer.byteLength of at least 37 bytes, containing the following fields:

  • rpIdHash (32 bytes) - A SHA256 hash of the relying party ID that was seen by the browser. The server will ensure that this hash matches a hash of its own origin in order to prevent phishing or other man-in-the-middle attacks.
  • flags (1 bytes) - A bitfield that indicates various attributes that were asserted by the authenticator. The bits are as follows, where "bit 0" is the least significant bit and all bits not specifically mentioned below are "reserved for future use":
    • Bit 0, User Presence (UP) - If set, authenticator validated that the user was present through some Test of User Presence (TUP), such as touching a button on the authenticator.
    • Bit 2, User Verification (UV) - If set, authenticator verified the actual user, through a biometric, PIN, or other authentication method.
    • Bit 6, Attested Credential Data (AT) - If set, attestedCredentialData will immediately follow the first 37 bytes of this authenticatorData.
    • Bit 7, Extension data (ED) - If set, extension data is present. Extension data will follow attestedCredentialData if it is present, or will immediatelly follow the first 37 bytes of the authenticatorData if no attestedCredentialData is present.
  • signCount (4 bytes) - A signature count from the authenticator. The server will use this counter to detect authenticator cloning.
  • attestedCredentialData (variable length) - The credential that was created. This is only present during a navigator.credentials.create() call. This is a sequence of bytes with the following format:
    • AAGUID (16 bytes) - Authenticator Attestation Globally Unique Identifier, a unique number that identifies the model of the authenticator (not the specific instance of the authenticator) so that a relying party can understand the characteristics of the authenticator by looking up its metadata statement.
    • credentialIdLength (2 bytes) - The length of the credential ID that immediately follows these bytes.
    • credentialId (variable length) - A unique identifier for this credential so that it can be requested for future authentications. The credential is "credentialIdLength" bytes long.
    • credentialPublicKey (variable length) - A COSE encoded public key. This public key will be stored on the server associated with a user's account and be used for future authentications.
  • extensions (variable length) - An optional CBOR map of extensions.


var options = {
  challenge: new Uint8Array(26), // will be another value, provided by the relying party server
  timeout: 60000

navigator.credentials.get({  publickey: options })
  .then(function (assertionPKCred) {
    var authenticatorData = assertionPKCred.response.authenticatorData;
    // Maybe try to convert the authenticatorData to see what's inside

    // Send response and client extensions to the server so that it can
    // go on with the authentication
}).catch(function (err) {


Specification Status Comment
Web Authentication: An API for accessing Public Key Credentials Level 1
The definition of 'authenticatorData' in that specification.
Recommendation Initial definition.

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
authenticatorDataChrome Full support 67
Full support 67
Full support 65
Notes Disabled
Notes Only supports USB U2F tokens.
Disabled From version 65: this feature is behind the Web Authentication API preference (needs to be set to Enabled). To change preferences in Chrome, visit chrome://flags.
Edge Full support 18Firefox Full support 60
Full support 60
Notes Only supports USB U2F tokens.
IE No support NoOpera No support NoSafari Full support 13WebView Android Full support 70Chrome Android Full support 70Firefox Android Full support 60
Full support 60
Notes Only supports USB U2F tokens.
Opera Android No support NoSafari iOS Full support 13.3Samsung Internet Android No support No


Full support  
Full support
No support  
No support
See implementation notes.
See implementation notes.
User must explicitly enable this feature.
User must explicitly enable this feature.