FormsAuthentication?

if( IsUserAuthenticated(txtUser, txtPassword) )
{
    // Create the authetication ticket

    FormsAuthenticationTicket authTicket new FormsAuthenticationTicket(1, txtUserName.Text, DateTime.Now, DateTime.Now.AddMinutes(60), False , groups);

    // Now encrypt the ticket.
    string encryptedTicket = FormsAuthentication.Encrypt(authTicket);

    // Create a cookie and add the encrypted ticket to the cookie as data.
    HttpCookie authCookie = new HttpCookie(FormsAuthentication.FormsCookieName, encryptedTicket);

    // Add the cookie to the outgoing cookies collection.
    Response.Cookies.Add(authCookie);

    // Redirect the user to the originally requested page
    Response.Redirect(FormsAuthentication.GetRedirectU  rl(txtUserName.Text,false));
}

if( IsUserAuthenticated(txtUser, txtPassword) )
{
    FormsAuthentication.RedirectFromLoginPage(txtUser.  Text, false);
}

FormsAuthentication.RedirectFromLoginPage(txtUser.    Text, Checkbox1.Checked);