<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl" %>
<%
    if (Request.IsAuthenticated) {
%>
        Welcome <b><%= Html.Encode(Page.User.Identity.Name) %></b>!
        [ <%= Html.ActionLink("Log Off", "LogOff", "Account") %> ]
<%
    }
    else {
%>
        [ <%= Html.ActionLink("Log On", "LogOn", "Account") %> ]
<%
    }
%>

<%= Html.LoginStatus() =>

/Views/Shared/LoginStatus.Anonymous.ascx
/Views/Shared/LoginStatus.Authenticated.ascx

<asp:LoginView Runat="Server">
    <LoggiedInTemplate>
        Welcome, <%= Html.Encode(Model.UserName) %>!
        <button>Sign Out</button>
    </LoggedInTemplate>
    <AnonymousTemplate>
        <button>Sign In</button> | <button>Join Now!</button>
    </AnonymousTemplate>
</asp:LoginView>

public ActionResult ShowAPage()
{
   if(!HttpContext.User.Identity.IsAuthenticated)
   {
      return RedirectToRoute("ShowLoginPage")
   }
   return View();
}

public ActionResult ShowAPage()
{
   if(!HttpContext.User.Identity.IsAuthenticated)
   {
      return View("ShowAPageView", "LoggedInMasterPageName");
   }
   return View("ShowAPageView", "LoggedOutMasterPageName");
}