Reviewer: Bo Wu
Review result: Has Nits

I am the assigned Ops reviewer for this draft. 

Document: draft-ietf-acme-subdomains-04

Summary:

This document (with intended status Standards Track) extends ACME [RFC8555] to support issuing certificates for subdomains. This is a well-written document.

Major issues: None.

Minor issues: None.

Nits/editorial comments:

1- Question: Section 4.3, Would it better to replace "a given identifier FQDN" with "a given subdomain"?
   Clients need a mechanism to optionally indicate to servers whether or
   not they are authorized to fulfill challenges against parent domains
   for a given identifier FQDN. 

2- Question: Section 5, it seems that the text below the call flow figure is not consistent with the figure. It would be better to describe the differences between the steps in the figure and the steps in the text below.

3- Inconsistent words: Section 5, pre-authorised -> pre-authorized

4- Question: Section 8, Is RFC 8555 a normal reference as this document is an enhancement to this RFC?

Thanks,
Bo Wu