/**
* Signs the form. This method may be overridden to import fields to be signed, just call Form::setHiddenValue()
* @return Form
*/
function sign(WebRequest $request)
{
Assert::isFalse($this->isSigned(), 'form already signed');
$this->privateValues['referrer'] = (string) $request->getHttpUrl();
$this->addControl(FormControl::hidden($this->getSignatureFieldName(), $this->exportSignature()));
$this->signed = true;
return $this;
}
