Custom domain support to cloudflare proxied domain

We have configured domain exmpl.io with Cloudflare.

Our customers want to point their domain abc.example.com to the exmpl.io, we asked to set up CNAME and point to exmpl.io.

But SSL is not working when exmpl.io is not proxied via Cloudflare, when proxied, the domain pointed is not working.

How can I give support for SSL to the domain proxied on Cloudflare?

You need to check out SSL for SaaS: