How do I require a login before a page is viewable?

Put a call to RequireLogin in the Page_Load routine:

    <script runat="server" id="scriptMain">
         
     Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
     
         Me.RequireLogin
        
     End Sub 
            
    </script>