inject-request-token.html

<script>
var form = document.getElementById('new_user')

form.onsubmit = function(e) {
  e.preventDefault();

  _castle('createRequestToken').then(function(requestToken) {
    // Populate a hidden field called `castle_request_token` with the
    // request token
    var hiddenInput = document.createElement('input');
    hiddenInput.setAttribute('type', 'hidden');
    hiddenInput.setAttribute('name', 'castle_request_token');
    hiddenInput.setAttribute('value', requestToken);

    // Add the hidden field to the form so it gets sent to the server
    // before submitting the form
    form.appendChild(hiddenInput);

    form.submit();
  });
};
</script>