Credential Management API Feature Detection Check-up

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Eiji Kitamura
Eiji Kitamura
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TL;DR #

WebAuthn helps increase security by bringing public-key credential based authentication to the Web, and is soon to be supported in Chrome, Firefox and Edge (with the updated spec). It adds a new kind of Credential object, which, however, may break websites that use the Credential Management API without feature-detecting the specific credential types they're using.

If you are currently doing this for feature detection #

if (navigator.credentials && navigator.credentials.preventSilentAccess) {
    // use CM API
}

Do these instead #

if (window.PasswordCredential || window.FederatedCredential) {
    // Call navigator.credentials.get() to retrieve stored
    // PasswordCredentials or FederatedCredentials.
}

if (window.PasswordCredential) {
    // Get/Store PasswordCredential
}

if (window.FederatedCredential) {
    // Get/Store FederatedCredential
}

if (navigator.credentials && navigator.credentials.preventSilentAccess) {
    // Call navigator.credentials.preventSilentAccess()
}

See changes made to the sample code as an example.

Read on to learn more.

What is the Credential Management API #

The Credential Management API (CM API) gives websites programmatic access to the user agent’s credential store for storing/retrieving user credentials for the calling origin.

Basic APIs are:

  • navigator.credentials.get()
  • navigator.credentials.store()
  • navigator.credentials.create()
  • navigator.credentials.preventSilentAccess()

The original CM API specification defines 2 credential types:

  • PasswordCredential
  • FederatedCredential

The PasswordCredential is a credential that contains user's id and password.
The FederatedCredential is a credential that contains user's id and a string that represents an identity provider.

With these 2 credentials, websites can:

  • Let the user sign-in with a previously saved password-based or federated credential as soon as they land (auto sign-in),
  • Store the password-based or federated credential the user has signed in with,
  • Keep the user's sign-in credentials up-to-date (e.g. after a password change)

What is WebAuthn #

WebAuthn (Web Authentication) adds public-key credentials to the CM API. For example, it gives websites a standardized way to implement second-factor authentication using FIDO 2.0 compliant authenticator devices.

On a technical level, WebAuthn extends the CM API with the PublicKeyCredential interface.

What is the problem? #

Previously we have been guiding developers to feature detect the CM API with following code:

if (navigator.credentials && navigator.credentials.preventSilentAccess) {
  // Use CM API
}

But as you can see from the descriptions above, the `navigator.credentials` is
now expanded to support public-key credentials in addition to password
credentials and federated credentials.

The problem is that user agents don't necessarily support all kinds of
credentials. If you continue feature detect using `navigator.credentials`, your
website may break when you are using a certain credential type not supported by
the browser.

**Supported credential types by browsers**
<table class="properties with-heading-tint"><tbody><tr>
<th></th>
<th>PasswordCredential / FederatedCredential</th>
<th>PublicKeyCredential</th>
</tr><tr><th>Chrome
</th><td>Available
</td><td>In development
</td></tr><tr><th>Firefox
</th><td>N/A
</td><td>Aiming to ship on 60
</td></tr><tr><th>Edge
</th><td>N/A
</td><td>Implemented with <a href="https://blogs.windows.com/msedgedev/2016/04/12/a-world-without-passwords-windows-hello-in-microsoft-edge/">older API</a>. New API (navigator.credentials) coming soon.
</td></tr></tbody></table>


## The solution
You can avoid this by modifying feature detection code as follows to explicitly
test for the credential type that you intend to use.

```js
if (window.PasswordCredential || window.FederatedCredential) {
    // Call navigator.credentials.get() to retrieve stored
    // PasswordCredentials or FederatedCredentials.
}

if (window.PasswordCredential) {
    // Get/Store PasswordCredential
}

if (window.FederatedCredential) {
    // Get/Store FederatedCredential
}

if (navigator.credentials && navigator.credentials.preventSilentAccess) {
    // Call navigator.credentials.preventSilentAccess()
}

See actual changes made to the sample code as an example.

For a reference, here's how to detect PublicKeyCredential added in WebAuthn:

if (window.PublicKeyCredential) {
    // use CM API with PublicKeyCredential added in the WebAuthn spec
}

Timeline #

Earliest available implementation of WebAuthn is Firefox and is planned to be stable around early May 2018.

Finally #

If you have any questions, send them over to @agektmr or agektmr@chromium.org.

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