Form Authentication

Hi,

I am new to Form Authentication. I want to check if the username and password is correct, then the user will redirect to Default.aspx otherwise still in Login.aspx

In web.config

<authentication mode="Forms"><forms loginUrl="Login.aspx" defaultUrl="Default.aspx" timeout="1800"></forms></authentication><authorization><deny users="?" /></authorization>

I am not using Login controls. Just place two textbox and button.

In Login.aspx.cs

protected void btnLogin_Click(object sender, EventArgs e)
        {

            AdminLogin objad = AdminLogin.GetAdminLogin(txtUserName.Text.Trim());
            if (objad == null)
            {

            }
            else
            {
                if (objad.Password == txtPassword.Text.Trim())
                {
                    Response.Redirect("Default.aspx");
                }
                else
                {
                    Utils.ShowAlert(this,"Invalid Username or Password");
                }
            }
        }

But still in Login.aspx If the username and Password is Correct. I need to know How to Configure Authentication in code behind.

Thanks.