Call app.UseReverseProxyHttpsEnforcer in your Startup.cs

Startup.cs

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory lf) {
    if (env.IsDevelopment()) {
        app.UseDeveloperExceptionPage();
    } else {
        app.UseExceptionHandler("/error");
        app.UseReverseProxyHttpsEnforcer();
    }

    app.UseAuthentication();
    app.UseStaticFiles();

    app.UseMvc(routes => {
        routes.MapRoute(
            name: "default",
            template: "{controller}/{action=Index}/{id?}");
    });
}