Cannot set a subdomain friendly cookie

Question

I have been trying to resolve this all afternoon and failed miserably.

I have a simply ASP.NET form deployed to an Azure Web App service and I am trying to set a subdomain friendly cookie to allow me to access the same cookie in other sub domains. My code on the button click is: -

protected void btnCookie_Click(object sender, EventArgs e)
{
    HttpCookie cookie = new HttpCookie("AndyTest", "Working");
    cookie.Domain = ".azurewebsites.net";
    Response.SetCookie(cookie);
}

I can then see in my response headers using Chrome dev tools the following: -

Set-Cookie: AndyTest=Working; domain=.azurewebsites.net; path=/

However there is a little warning triangle next to it and it says: -

This Set-Cookie was blocked because its Domain attribute was invalid with regards to the current host url

I look at the Host request headers and this is as follows: -

Host: skqmwq-auth3.azurewebsites.net

So everything looks to be setup correctly but I can't get it to work. I have also looked at a similar cookie in another application and it is set up identically to the above and works fine. Hence I assume it must be some kind of environment related configuration causing the error to be displayed by Chrome.

Answer 1

Well after spending hours and hours on this I stumbled across this post on StackOverflow

https://stackoverflow.com/a/52475993/10529344

There is a list of domain names that you cannot create sub domain cookies against, https://publicsuffix.org/list/public_suffix_list.dat not that chrome tells you that your domain is on this list, that would be way too easy.

I simply configured my CNAME's and hey presto my cookies now work!