Custom sign out page, not removing cookies

Question

In my custom login script I'm creating a cookie that can be read by other company web applications. The code for this is:

setCookie("Communities", "LoggedIn=true&NSContactId=" + NSContactId, ".mydomain.com");

where

public static void setCookie(string cookieName, string cookieValue, string cookieDomain)
{
    HttpCookie newCookie = new HttpCookie(cookieName);
    newCookie.Value = cookieValue;
    newCookie.Expires = DateTime.Now.AddDays(30);
    newCookie.Domain = cookieDomain;
    HttpContext.Current.Response.Cookies.Add(newCookie);
}

I need to remove this custom cookie when someone logs out of SharePoint, and I'm having trouble with this.

I created a custom signout page (mylogout.aspx), and replaced the default one with this custom one, using the following:

Set-SPCustomLayoutPage -Identity SignOut -RelativePath "/_layouts/mylogout.aspx" -WebApplication "http://sp.mydomain.com"

and "mylogout.aspx" uses this code:

<%
HttpCookie CommunitiesCookie = new HttpCookie("Communities");
CommunitiesCookie.Value = null;
CommunitiesCookie.Domain = ".mydomain.com";
CommunitiesCookie.Expires = DateTime.Now.AddDays(-1);
Response.Cookies.Add(CommunitiesCookie);
Response.Redirect("/_layouts/signout.aspx");
%>

I know the code is being run (I can put in a line of code to write to a log file, and it does so), but the cookie doesn't get removed. I've used this code in non-SharePoint sites before, and it works there, so I'm left assuming that something in SharePoint is stopping this from working.

Any ideas?

Answer 1

Have you used a tool like Fiddler to view the HTTP traffic and the requests the browser is making? It might be worth checking to see if the browser is requesting /_layouts/signout.aspx and redirecting back to the login page and reauthenticating. What type of security do you have on signout.aspx vs mylogout.aspx?