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

extensions, an optional property of the PublicKeyCredentialCreationOptions dictionary, is an object providing the client extensions and their input values.

Extensions are values requesting additional processing by the client and by the authenticator. For instance, extensions may be used for:

  • backward compatibility with the legacy FIDO JS API,
  • knowing the user verification process,
  • etc.

Note: An analogous option exists for the fetching operation (navigators.credentials.get()), see PublicKeyCredentialRequestOptions.extensions.


extensions = publicKeyCredentialCreationOptions.extensions


An object with various keys and values.

Here is the current (as of March 2019) list of potential extensions which may be used during the registration operation.

Warning: As of June 2020, only appId (used during creation with PublicKeyCredentialRequestOptions.extensions) is supported by Chrome and Edge. Firefox does not seem to support any extension. Also Chrome doesn't plan to support any other extension in future

Extension identifier Type Description
authnSel Array of BufferSource Authenticator selection. Restricts the list of authenticator models which may be used. If no matching authenticator is available, the credential is still generated with another available authenticator.
exts Boolean Supported extensions. If true, the client outputs an array of strings containing the extensions which are supported by the authenticator.
uvi Boolean User verification index. If true, the client outputs an ArrayBuffer which contains a value uniquely identifying a user verification data record. In other words, this may be used server side to check if the current operation is based on the same biometric data that the previous authentication.
loc Boolean Location. If true, the client outputs a GeolocationCoordinates object representing the geolocation of the authenticator.
uvm Boolean User verification method. If true, the client outputs an array of arrays with 3 values containing information about how the user was verified (e.g. fingerprint, pin, pattern), how the key is protected, how the matcher (tool used for the authentication operation) is protected.
biometricPerfBounds Object with two numerical properties: FAR and FRR Biometric authenticator performance bounds. The client must not use any authenticator with false acceptance rate (FAR) and false rejection rate (FRR) below the inputs. The client outputs true if this was taken into account.

Note: Extensions are optional and different browsers may recognize different extensions. All extensions are optional for the client to process them: if a browser does not know a given extension, that will not cause any failure, the extension will not be processed.


var publicKey = {
    uvi: true,
    loc: false,
    uvm: false,
    exts: true
  challenge: new Uint8Array(26) /* this actually is given from the server */,
  rp: {
    name: "Example CORP",
    id  : ""
  user: {
    id: new Uint8Array(26), /* To be changed for each user */
    name: "",
    displayName: "John Doe",
  pubKeyCredParams: [ {
    type: "public-key",
    alg: -7 } ]

navigator.credentials.create({ publicKey })
  .then(function (newCredentialInfo) {
    // myBuffer will contain the result of any of the processing of the extensions
    var myBuffer = newCredentialInfo.getClientExtensionResults();

    // send attestation response and client extensions
    // to the server to proceed with the registration
    // of the credential
  }).catch(function (err) {


Web Authentication: An API for accessing Public Key Credentials - Level 3 (Web Authentication)
# dom-publickeycredentialcreationoptions-extensions

Browser compatibility

BCD tables only load in the browser

See also