When I try
user = System.Web.UI.Page.CurrentUser
or
user = System.Web.UI.Page.User.Identity
I get an erro
CurrentUser doesn't seem to be a property on System.Web.UI.Page. (http://msdn.microsoft.com/en-us/library/system.web.ui.page.aspx)
Your controller should expose a property named User, does that work? For example:
var user = User;