PublicKeyCredential: isConditionalMediationAvailable() static method

The isConditionalMediationAvailable() static method of the PublicKeyCredential interface returns a Promise which resolves to true if conditional mediation is available.

Conditional mediation, if available, results in any discovered credentials being presented to the user in a non-modal dialog box along with an indication of the origin requesting credentials. This is requested by including mediation: 'conditional' in your get() call. In practice, this means autofilling available credentials; you need to include autocomplete="webauthn" on your form fields so that they will show the WebAuthn sign-in options.

A conditional get() call does not show the browser UI and remains pending until the user picks an account to sign-in with from available autofill suggestions:

• If the user makes a gesture outside of the dialog, it closes without resolving or rejecting the Promise and without causing a user-visible error condition.
• If the user selects a credential, that credential is returned to the caller.

The prevent silent access flag (see CredentialsContainer.preventSilentAccess()) is treated as being true regardless of its actual value: the conditional behavior always involves user mediation of some sort if applicable credentials are discovered.

isConditionalMediationAvailable()

// Availability of `window.PublicKeyCredential` means WebAuthn is usable.
if (window.PublicKeyCredential &&
    PublicKeyCredential.​​isConditionalMediationAvailable) {
  // Check if conditional mediation is available.
  const isCMA = await PublicKeyCredential.​​isConditionalMediationAvailable();
  if (isCMA) {
    // Call WebAuthn authentication
    const publicKeyCredentialRequestOptions = {
      // Server generated challenge
      challenge: ****,
      // The same RP ID as used during registration
      rpId: 'example.com',
    };

    const credential = await navigator.credentials.get({
      publicKey: publicKeyCredentialRequestOptions,
      signal: abortController.signal,
      // Specify 'conditional' to activate conditional UI
      mediation: 'conditional'
    });
  }
}