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

extensions, an optional property of the PublicKeyCredentialRequestOptions 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 creation operation (navigators.credentials.create()), see PublicKeyCredentialCreationOptions.extensions.


extensions = publicKeyCredentialRequestOptions.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 March 2019, only appid is supported by Chrome and Edge. Firefox does not seem to support any extension.

Extension identifier Type Description
appid USVString FIDO appID. An appID which was used with legacy FIDO JS APIs to identify the current relying party.
txAuthSimple USVString Simple transaction authorization. This text is displayed on a prompt of the authenticator before verifying the user or testing their presence. The client outputs a USVString which is the text as it was displayed (line breaks may have been added).

An object with two properties:

Generic transaction authorization. This is used to display an image or some non-textual content on the authenticator before verifying the user or testing their presence. The contentType gives the MIME type of the resource to be displayed while content gives its actual content. The client outputs the hash of the content which was displayed (hashing with the same algorithm which is used for the signature).
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 Coordinates 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.

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 simply will not be processed.


var options = {
  extensions: {
    uvm: true,
    loc: false,
    txAuthSimple: "Could you please verify yourself?"
  challenge: new Uint8Array([/* bytes sent from the server */])

navigator.credentials.get({ "publicKey": options })
    .then(function (credentialInfoAssertion) {
    // send assertion response back to the server
    // to proceed with the control of the credential
}).catch(function (err) {


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

Browser compatibility

Update compatibility data on GitHub
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Chrome Full support 67Edge ? Firefox Full support 60IE ? Opera Full support YesSafari ? WebView Android ? Chrome Android ? Edge Mobile ? Firefox Android ? Opera Android Full support YesSafari iOS ? Samsung Internet Android ?


Full support  
Full support
Compatibility unknown  
Compatibility unknown
Experimental. Expect behavior to change in the future.
Experimental. Expect behavior to change in the future.

See also

Document Tags and Contributors

Contributors to this page: billinghamj, SphinxKnight, mdnwebdocs-bot
Last updated by: billinghamj,