@Override
    protected void onError(final RequestContext requestContext) {
        WebUtils.putCasLoginFormViewable(requestContext,
            WebUtils.isCasLoginFormSetToViewable(requestContext) || casProperties.getAuthn().getX509().isMixedMode());
        requestContext.getRequestScope().put(REQUEST_ATTRIBUTE_X509_ERROR, "true");
    }
Concrete implementation of AbstractNonInteractiveCredentialsAction that
obtains the X509 Certificates from the HttpServletRequest and places them in
the X509CertificateCredential.

@author Scott Battaglia
@since 3.0.0
support/cas-server-support-x509-webflow/src/main/java/org/apereo/cas/web/flow/X509CertificateCredentialsRequestHeaderAction.java