Foros del web, para los que viven de bits

 Response.Redirect("paginaDestino.aspx?nombre="+TextBox1.Text);

Label1.Text = "Bienvenido " + Request.Params["nombre"];

....
FormsAuthentication.Initialize()
                    ' Se crea el ticket con el rol que le corresponda
                    Dim ticket As New FormsAuthenticationTicket(1, _
                            nombreUsuario, DateTime.Now, _
                            DateTime.Now.AddMinutes(20), _
                            True, roles, _
                            FormsAuthentication.FormsCookiePath)
                    ' Se encripta el ticket
                    Dim encTicket As String = FormsAuthentication.Encrypt(ticket)
                    ' Se crea la cookie con el ticket encriptado
                    Dim cookie As New HttpCookie(FormsAuthentication.FormsCookieName, encTicket)
                    ' Caducidad de la cookie igual que el ticket
                    'cookie.Expires = ticket.Expiration
                    ' Se envía la cookie
                    Response.Cookies.Add(cookie)
                    ' Se redirige al usuario
                    Response.Redirect(Request.QueryString("ReturnUrl"))
...

Dim nombreUsuario As String = Context.User.Identity.Name

    Sub Application_AuthenticateRequest(ByVal sender As Object, ByVal e As EventArgs)
        ' Se desencadena al intentar autenticar el uso
        If Not (HttpContext.Current.User Is Nothing) Then
            If HttpContext.Current.User.Identity.IsAuthenticated Then
                If TypeOf HttpContext.Current.User.Identity Is FormsIdentity Then
                    Dim id As FormsIdentity = CType(HttpContext.Current.User.Identity, FormsIdentity)
                    Dim ticket As FormsAuthenticationTicket = id.Ticket
                    Dim userData As String = ticket.UserData
                    Dim roles() As String = userData.Split(",")
                    HttpContext.Current.User = New GenericPrincipal(id, roles)
                End If
            End If
        End If
    End Sub