Using the Security helper, FormSignature calculates a hash of all fields in a form, so that
when the form is submitted, the fields may be validated to ensure that none were added or
removed, and that fields designated as _locked_ have not had their values altered.
To enable form signing in a view, simply call $this->security->sign() before generating your
form. In the controller, you may then validate the request by passing $this->request to the
check() method.