done = function(index, max, _, resp) {
    if (index == max && opt_callback) {
      opt_callback(resp);
    }
  }
Process a SPF response on the current page outside of a navigation flow.

@param {spf.SingleResponse|spf.MultipartResponse} response The SPF response
    object to process.
@param {function((spf.SingleResponse|spf.MultipartResponse))=} opt_callback
    Function to execute when processing is done; the argument is
    the `response`.