Cloudflare is compatible with websites using SSL using Cloudflare’s Universal SSL.
Once you have enabled Cloudflare on your domain, you’ll be able to adjust the Cloudflare SSL configuration settings from the Cloudflare dashboard, or by using the cPanel plugin.
Note that GreenGeeks suggests using “Full” SSL with a certificate installed within your GreenGeeks cPanel to encrypt connections between GreenGeeks & the Cloudflare network.