private static HttpResponse fail(ServiceRequestContext ctx, Throwable cause) {
        logger.trace("{} Cannot initiate SAML authentication", ctx, cause);
        return HttpResponse.of(HttpStatus.UNAUTHORIZED);
    }
Returns an {@link HttpResponse} for SAML authentication failure.
saml/src/main/java/com/linecorp/armeria/server/saml/SamlDecorator.java