Bind custom domain to subdomain with Laravel

I have a website build with Laravel 5.4.

Where user signs up and create an app, then each app gets a subdomain like this:

http://app1.domain.com

Question:

Can user bind a custom domain to app1.domain.com useing CNAME?

What should I do in my routes to stand this?

I tried this:

In my app tables, have domain column. And demo.doamin.com alrady CNAME to app1.domain.com.

But when i visit demo.domain.com, I got a blank page..

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