Change effective on 21 March 2017
All apps with paid dynos (Hobby, Standard-1X, Standard-2X, Performance-M, and Performance-L) now have access to Automated Certificate Management (ACM).
With Automated Certificate Management, Heroku automatically manages TLS certificates for all apps that have Hobby and Professional dynos on the Common Runtime. Certificates handled by ACM automatically renew before they expire, and new certificates are created automatically whenever you add or remove a custom domain.
For more information on how to set this up on your applications, please see our Dev Center article.