It's easy to use https with cloudflare setup. As long as you click on the proxied logo you can access via https.
You have to buy a SSL certificate for your subdomain and give us your certificate info so we can install on our game server.
Useful tools if you do not know how to buy one:
Namecheap CSR Generator: https://decoder.link/csr_generator
We recommend buying on Namecheap or https://comodosslstore.com/positivessl.aspx
Just get the cheapest PositiveSSL.