One of the services Cloudflare provides for our Enterprise customers is the Custom Hostname service (also known as SSL for SaaS). This service lets another website owner create a CNAME that targets your domain on Cloudflare and Cloudflare will resolve with the CNAME zone's host header.
The main benefit to a Custom Hostname setup is to preserve branding for a Cloudflare customer. For an SaaS company, a client who signs up for your service does not need to make a separate Cloudflare account. The customer can use the SaaS provider’s account to add the benefits Cloudflare adds to your website. This allows a SaaS company to add clients with relative ease.
Since Cloudflare's features are all applied to a zone on an account there are some extra things to consider:
Requests with host headers that don't belong to the managed zone cannot be directly managed by this zone in the Cloudflare UI or via the API.
This means that page rules cannot be created by the site owner for zones CNAME’d to their domain unless using Edge Side Code.
Files for zones CNAME’d to the domain on CloudFlare will be cached based on our default caching behaviors (file extensions, duration, etc.).
Files for zones CNAME’d to the domain on Cloudflare can only be purged using the cache tag functionality.