Cloudflare may issue certificates for SSL products from any of the
following Certificate Authorities (CAs):
- Let’s Encrypt
- Sectigo (formerly Comodo)
I also found this recent Cloudflare community post:
michael MVP '20 - '21
Cloudflare use multiple certificate authorities, including Let’s
Encrypt. These certs are independent of any certs on your origin,
which you should continue to maintain with your acme.sh script.
domjh liked this
There is a blog post from March 27, 2021 explaining one way to get a cert signed by LE or Digicert:
Introducing: Advanced Certificate Manager
Apart from the security features that ACM has to offer, we are excited
to give our customers an easy-to-use and configurable certificate
management solution. With ACM, customers will now be able to issue up
to 100 edge certificates per zone, which includes the zone apex and up
to 50 hostnames. This means your certificate now has multi-level
support, so you can create certificates for second and third-level
hostnames. In addition, customers will be able to choose their
preferred validation method (HTTP, TXT, or Email) and their
certificate authority (Let’s Encrypt or Digicert).
There is probably more in their docs that I didn't find.