Cookies not being set by IIS in HTTP header - asp.net

Question

I use ASP.NET forms authentication that seems to work ok online but not in my development environment for Internet Explorer, Firefox, and Chrome. As far as I can see IIS is not sending the Set-Cookie HTTP header when a page is being requested:
GET http://127.0.0.1:81/ HTTP/1.1
Accept: text/html, application/xhtml+xml, */*
Accept-Language: nb-NO
User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; Trident/7.0; rv:11.0) like Gecko
Accept-Encoding: gzip, deflate
Host: 127.0.0.1:81
DNT: 1
Connection: Keep-Alive
HTTP/1.1 200 OK
Cache-Control: private
Content-Type: text/html; charset=utf-8
Vary: Accept-Encoding
Server: Microsoft-IIS/8.0
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
Date: Wed, 08 Oct 2014 19:24:58 GMT
Content-Length: 13322
I've tried adding 127.0.0.1 www.example.com to the \Windows\System32\drivers\etc\hosts file and accessing http://www.example.com:81 instead, but that has no effect. Here are my web.config settings:
<!-- ASP.NET forms authentication is enabled by default -->
<authentication mode="Forms">
<!-- Set the page to redirect to when the user attempts to access a restricted resource -->
<forms loginUrl="~/Account/Login.aspx" timeout="2880" />
</authentication>

Answer 1

I've found a work-around by always setting a dummy cookie if no cookies are sent inside the ASP.NET web page:
/// <summary>
/// Force the browser to use cookies if none are in use.
/// Sets an empty cookie.
/// </summary>
void ForceCookiesIfRequired()
{
if (Request.Cookies == null || Request.Cookies.Count == 0)
{
// No cookies, so set a dummy blank one
var cookie1 = new HttpCookie(FormsAuthentication.FormsCookieName, String.Empty) { Expires = DateTime.Now.AddYears(-1) };
Response.Cookies.Add(cookie1);
}
}
protected override void OnInit(EventArgs e)
{
base.OnInit(e);
// Force the use of cookies if none are sent
ForceCookiesIfRequired();
}
I never had todo this before, has some Microsoft patch or upgrade broken ASP.NET forms authentication? One way to check your own solutions is to clear the cookie I guess. This forces the Set-Cookie HTTP header to be sent by the IIS server.