<authentication mode="Forms" >
  <forms name="logon" path="/" loginUrl="~/logon.aspx" protection="All" timeout="75"/>
  </authentication >
  <authorization>
    <deny users="?"/>
  </authorization>

protected void Button1_Click(object sender, EventArgs e)
  {
     if (TextBox1.Text == "varun" && TextBox2.Text == "v")
     {            
      FormsAuthentication.RedirectFromLoginPage(TextBox1.Text,
      CheckBox1.Checked);     
  }

        FormsAuthentication.SignOut();
        Response.Redirect("logon.aspx");