Where Do I get Certificate For Heroku Wildcard Domain?

Question

I am building an app and I want to use a wildcard domain (e.g. *.domain.com). In order to add this domain to Heroku, I need to obtain a wildcard SSL certificate and import it manually to Heroku. I am using Cloudflare as my domain provider. Where can I obtain a wildcard SSL certificate for this purpose, and how do I go about importing it to Heroku?