btcpayserver/BTCPayServer/Views/Account/LoginWithU2F.cshtml

@model BTCPayServer.U2F.Models.LoginWithU2FViewModel

<form id="u2fForm" asp-action="LoginWithU2F" method="post" asp-route-returnUrl="@ViewData["ReturnUrl"]">
    <input type="hidden" asp-for="Version" />
    <input type="hidden" asp-for="Challenge" />
    <input type="hidden" asp-for="AppId" />
    <input type="hidden" asp-for="DeviceResponse" />
    @for (int i = 0; i < Model.Challenges.Count; i++)
    {
        @Html.HiddenFor(m => m.Challenges[i])
    }
    <input type="hidden" asp-for="UserId" />
    <input type="hidden" asp-for="RememberMe" />
</form>

<section class="pt-5">
    <div>
        <div class="row">
            <div class="col-lg-12 section-heading">
                <h2>U2F Authentication</h2>
                <hr class="primary">
                <div>
                    <span id="spinner" class="fa fa-spinner fa-spin float-right ml-3 mr-5 mt-1" style="font-size:2.5em"></span>
                    <p>Insert your U2F device or hardware wallet into your computer's USB port. If it has a button, tap on it.</p>
                </div>
                <p id="error-message" class="d-none alert alert-danger"></p>
                <a id="btn-retry"  class="btn btn-secondary d-none" href="javascript:window.location.reload()">Retry</a>
            </div>
        </div>
    </div>
</section>

<script src="~/vendor/u2f/u2f-api-1.1.1.js" asp-append-version="true"></script>
<script type="text/javascript">
    document.addEventListener("DOMContentLoaded", () => {
        window.u2fApi.sign(
            @Safe.Json(Model.Challenges)
        )
        .then(data => {
            document.getElementById("DeviceResponse").value = JSON.stringify(data);
            document.getElementById("u2fForm").submit();
        })
        .catch(error => {
            document.getElementById("error-message").innerText = error.message;
            document.getElementById("error-message").classList.remove("d-none");
            document.getElementById("spinner").classList.add("d-none");
            if (!error.message.endsWith("not supported")) {
                document.getElementById("btn-retry").classList.remove("d-none");
            }
        });
    });
</script>