Logout code in asp.net c# for admin which have master page

Onclick of logout button, redirect user to logout.aspx page. Add following code in logout.aspx page.

protected void Page_Load(object sender, EventArgs e)
    {
        Session.Abandon();
        
        Response.Redirect(clsCommon.value("login.aspx?mode=logout");
    }

http://www.dotnetfunda.com/codes/code1651-prevent-back-button-after-logout-in-aspnet.aspx[^]

You can use ASP.NET Login control if you are using Forms authentication that will take care of Logout

http://www.c-sharpcorner.com/uploadfile/raj1979/login-control-in-Asp-Net-3-5/[^]

protected void LogIn_Click(object sender, EventArgs e)
{
Session.Add("uname", txtUname .Text );
Session.Add("pass", txtPass .Text );
DataTable dt = BusinessLayer.GetData("select * from tblLogin where uid='" + txtUname .Text + "' and Upwd='" + txtPass .Text + "'");
if (dt.Rows.Count == 0)
{
//lblmessage.Text = "Invalid username or password";
Response.Write("<script language=javascript>alert('You Are Invalid User')</script>");
Response .Redirect ("Home.aspx");
}
}

protected void lnkbtnlogout_Click(object sender, EventArgs e)
   {
       Session.Abandon();
       Session.Clear();
       Response.Redirect("~/Default.aspx");
   }

Use a javascript block on top of each page which check the login state every time the page load. This force a login state check too even the user press the [Back] button of the browser.