Heroku https://www redirect to https://
You can't do the redirect at the DNS level for the www record, you'd need to redirect at the app. The reason is that if the redirect is at your DNS provider then the client browser will connect to https www.site.com but your DNS provider will not have a valid cert for your domain and the request will be refused by your browser, assuming of course that your DNS provider has port 443 open - which they sound like they don't.