Loggin User Status

I have serveral application, each with a unique domain, however I want to share the logged on user identification between applications.  I have a simple check for logged on users on the 'restricted' pages, and redirect non-logged in users to a login page.  All this works just fine within an application, but when I want to move from application (folder B) "B" to an equal (Folder C) application "c", the login fails.
All application are on the same host and are equal sub folders.
How can I pass login user information between these applications?
John
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load 'Check for UserName If Context.User.Identity.Name Is Nothing Or IsDBNull(Context.User.Identity.Name) Or Context.User.Identity.Name = String.Empty Then Response.Redirect("Login2.aspx") End If end sub
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