How can I stop a request in the PreAuthenticationMiddleware?

[ildoc]

I have to do some checks on the request's jwt before ocelot authentication, so I'm doing them within the PreAuthenticationMiddleware like this:

    var config = new OcelotPipelineConfiguration
    {
        PreAuthenticationMiddleware = async (ctx, next) =>
        {
            var jwt = ctx.HttpContext.Request.Headers["Authorization"];

            if (jwtIsOk(jwt)) next.Invoke();
            // else ...
        }
    };

    app.UseOcelot(config).Wait();

Instead of not-invoking next, is it possible to return a custom response?
I'd like to return a 401 error