How to write at the end of response stream asp-net

I want to add a variable at the end of each Response .

So in the base page handler i written some thing like this

protected override void OnPreRenderComplete(EventArgs e)
    {
        base.OnPreRenderComplete(e);

        Response.Write(String.Format("<script> var reqId=\"{0}\"</script>", "cgAAAF66S8U0gNQI");
    }

The variable is appended at the beginning of the response. when it renders on the browser , chrome reporting as

This page includes a password or credit card input in a non-secure context. A warning has been added to the URL bar

How i can append that to response stream so that it renders properly on to the browser. MY application is build on asp.net

I Don't user server side controls. All my controls are client side. I tried some this like this

In the OnloadComplete I didn't see any thing in the source code in the browser.

protected override void OnLoadComplete(EventArgs e)
{
base.OnLoadComplete(e);
Page.ClientScript.RegisterClientScriptBlock(GetType(), "reqIdScriptq", string.Format("var reqIqd=\"{0}\"", "cgAAAF66S8U0gNQI"), true);
ClientScript.RegisterHiddenField("abc", "def");
}