You can get free SSL from CloudFlare and connect it with the free SSL option at https://yourApp.herokuapp.com. (That's what I use at https://www.learneroo.com)
By default Heroku offers a wildcard SSL certificate which only covers
‘*.herokuapp.com’. This means that ‘Full SSL’ can be utilized as a default,
which does not require that the SAN contains your FQDN. To utilize
Full (Strict) you will need to add your own SSL certificate to your
Heroku app, which can be done by using their ‘SSL Endpoint’ add-on.
https://support.cloudflare.com/hc/en-us/articles/205893698-C...