This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The additionalData property of the PasswordCredential interface takes one of a FormData instance, a URLSearchParams instance, or null. The data in the objects will be added to the request body and sent to the remote endpoint with the credentials.


passwordCredential.additionalData = formData
formData = passwordCredential.additionalData
passwordCredential.additionalData = urlSearchParams
ulrSearchParams = passwordCredential.additionalData


One of a FormData instance, a URLSearchParams instance, or null.


The following example creates a FormData object with an appended CSRF token. It then stores the form object in the additionalData parameter before sending it to server in a call to fetch.

//The options object was previously created. 
navigator.credentials.get(options).then(function(creds) {
  if (creds.type == 'password') {
    var form = new FormData();
    var csrf_token = document.querySelector('csrf_token').value;
    form.append('csrf_token', csrf_token);

    creds.additionalData = form;

    fetch('', {
      method: 'POST',
      credentials: form


Specification Status Comment
Credential Management Level 1 Editor's Draft Initial definition.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 51.0 ? ? ? ?
Feature Android Android Webview Firefox Mobile (Gecko) Firefox OS IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support No support 51.0 ? ? ? ? ? 51.0


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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

additionalData API credential management credentials PasswordCredential Reference