@ExceptionHandler(MissingSamlAuthnRequestException.class)
    protected ModelAndView handleMissingAuthnRequest(final HttpServletRequest req, final Exception ex) {
        return WebUtils.produceErrorView(SamlIdPConstants.VIEW_ID_SAML_IDP_ERROR, ex);
    }
Handle SAML2 exceptions.

@param req the req
@param ex  the ex
@return the model and view
support/cas-server-support-saml-idp-web/src/main/java/org/apereo/cas/support/saml/web/idp/profile/AbstractSamlIdPProfileHandlerController.java