You want users go to a URL on the local domain and webserver and then redirect them to the Cloud tenant.
Create a simple index.html (or index.htm) web page on your own web server, using content similar to the below example.
Change the two URLs highlighted in the example below to reflect your tenant's URL. Your users will be redirected in the amount of seconds in the content="1; portion - in this case, 1 second.
Customize the page as needed (colors/images/Logos/etc) to meet your own internal requirements.
<title>Redirect to HeatSoftware Cloud after 1 second</title>
<meta http-equiv="refresh" content="1; URL=https://your-cloud-tenant.saasit.com/Login.aspx">
<meta name="keywords" content="automatic redirection">
If your browser doesn't automatically go there within a few seconds,
you may want to go to
<a href="https://your-cloud-tenant.saasit.com/Login.aspx"> Connect</a>