chromium/third_party/blink/web_tests/http/tests/credentialmanagement/resources/iframed-credentialscontainer.html

<!DOCTYPE html>
<script>

navigator.credentials.get({ 'password': true })
    .then(c => {
        window.top.postMessage({
            "credential": c,
            "exception": null
        }, "*");
    })
    .catch(omg => {
        window.top.postMessage({
            "credential": null,
            "exception": omg.name
        }, "*");
    });

navigator.credentials.store(new PasswordCredential({'id': 'name', 'password': 'password' }))
    .then(c => {
        window.top.postMessage({
            "credential": c,
            "exception": null
        }, "*");
    })
    .catch(omg => {
        window.top.postMessage({
            "credential": null,
            "exception": omg.name
        }, "*");
    });

navigator.credentials.preventSilentAccess()
    .then(_ => {
        window.top.postMessage({
            "preventSilentAccess": true,
            "exception": null
        }, "*");
    })
    .catch(omg => {
        window.top.postMessage({
            "preventSilentAccess": false,
            "exception": omg.name
        }, "*");
    });
</script>