Hit a roadblock while implementing a sub domain based language switcher (en.domain.com loads English, jp.domain.com loads Japanese).
How do I get a single member
Try creating the cookie yourself.
In AccountController you'll find this:
FormsAuthentication.SetAuthCookie(userName, createPersistentCookie);
that "creates and adds to the cookie collection". It doesn't allow modification of the domain (but does allow modification of the path, oddly). Instead create a cookie without adding to the collection, modify the necessary properties, then add to the collection:
var a = FormsAuthentication.GetAuthCookie(userName, createPersistentCookie);
//if you're debugging right here, a.Domain should be en.example.com; change it
a.Domain = "example.com";
HttpContext.Current.Response.Cookies.Add(a);
James