I created a login page then using .cfm page to save the data and redirect the page to main site. We are going to use subdomain page for marketing and I have everything else going. I just can't keep user logged in when the redirect to the main site.
This analogy suggests a solution. Countries share a common system to check passports. By analogy, the subdomain and main site are both your applications, and presumably share the same database.
You could use a session-based database table as follows.When a user successfully logs in on the ColdFusion site, their session is stored, for example, as a UUID. When opening a URL on the other site, the user passes the UUID. The second site will then validate it by comparing it with the value in the database.