How to disable browser cache in ASP.NET core rc2?

Try adding an Expires header as well:

app.UseStaticFiles(new StaticFileOptions()
{
    OnPrepareResponse = context =>
    {
        context.Context.Response.Headers.Add("Cache-Control", "no-cache, no-store");
        context.Context.Response.Headers.Add("Expires", "-1");
    }
});

Another approach would be to add a querystring that changes to the end of your requests in development. Middleware would not be required in this case.

<environment names="Development">
    <link rel="stylesheet" href="https://stackoverflow.com/questions/38231739/~/lib/bootstrap/dist/css/bootstrap.css?@DateTime.Now.Ticks" />
    <link rel="stylesheet" href="~/css/site.css?@DateTime.Now.Ticks" />
</environment>