ASP.NET Subdomain Cookie (parent and one subdomain)

Question

I have an app with multiple subdomains, subone.parent.com, subtwo.parent.com.

I have a logon page at parent.com/login. When a user logs in I redirect them to the proper domain based on which one they are a member of. This works fine.

FormsAuthenticationTicket ticket = new FormsAuth...
string encTicket = FormsAuthentication.Encrypt(ticket);
var cookie = new HttpCookie(FormsAuthentication.FormsCookieName, encTicket);
cookie.Domain = subone.parent.com
Response.Cookies.Add(cookie)

This properly authenticates the user for subone.parent.com and not subtwo.parent.com. However I would like to do the following.

If the user goes back to parent.com, I would like to know that they are logged in and redirect them back to subone.parent.com.

Is there a best practice for accomplishing this? Or do I have to set another cookie for parent.com?

I'm working in asp.net mvc if it matters.

THanks!

Answer 1

You can share cookies across domains like you are trying to do, but its not straight forward, example here.

Another options is to set the cookie to be ".parent.com" rather than specifying the sub-domain explicitly and use the cookie store the details of the sub-domain. Then you can access the cookie from any of your sub-domains (and parent assuming its www.parent.com).

If your using MVC, you can pretty easily create a custom filter and add to the www.parent.com controllers to check for the existence of the cookie, and if so redirect to the sub domain the cookie specifies. Further details of filters here.