The following code example uses the IsAuthenticated property to determine whether the current request has been authenticated. If it has not been authenticated, the request is redirected to another page where users can enter their credentials into the Web application. This is a common technique used in the default page for an application.

Private Sub Page_Load(sender As Object, e As EventArgs)
    ' Check whether the current request has been
    ' authenticated. If it has not, redirect the 
    ' user to the Login.aspx page.
    If (Request.IsAuthenticated = False) Then
        Response.Redirect("Login.aspx")
    End If
End Sub

private void Page_Load(object sender, EventArgs e)
{
    // Check whether the current request has been
    // authenticated. If it has not, redirect the 
    // user to the Login.aspx page.
    if (!Request.IsAuthenticated)
    {
        Response.Redirect("Login.aspx");
    }
}

Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

.NET Framework

Reference