FBA login page issue in SharePoint

Question

I have FBA sharepoint site with custom login code (see below). When the user login out side system and I passing Cookie value to FormsAuthentication.RedirectFromLoginPage(userName, false);. It works fine till here.

The issue is, If user goes out side the system and signed out and logged in with different user id and comes to my SharePoint site the login process is skipped and the user is logged in with old id (not with new login id).

Is there any way we can go through login process if user type sharepoint site url and redirected to shareoint site.

Please gurus help me out.

    try
    {
        if (Request.Cookies[authCookie].Value.Length > 0 || Request.Cookies[authCookie].Value != null || Request.Cookies[authCookie].Value != "")
        {
            userName = Request.Cookies[authCookie].Value;
        }
    }
    catch (Exception ex)
    {
        Response.Redirect("https://qa.company.com/appssecured/login/servlet/LoginServlet?TARGET_URL=" + Request.Url);
    }
    if (true)
    {
        userName = Request.Cookies[authCookie].Value;
        FormsAuthentication.RedirectFromLoginPage(userName, false);
    }

Web.Config

<authentication mode="Forms">
  <forms loginUrl="LoginAuth.aspx" timeout="2880" enableCrossAppRedirects="false" />
  <!--      <forms loginUrl="/_layouts/login.aspx" />-->
</authentication>

Answer 1

Why not use

FormsAuthentication.SignOut();
FormsAuthentication.RedirectToLoginPage();

This should clear the cookie properly and redirect to login page.