It turns out that it is impossible to remove the charset=utf-8
from the content-type header sent by Wordpress or Github, or any other HTTP spec compliant webserver, for that matter. Since Microsoft is not HTTP compliant, their own webserver can do this (by breaking the HTTP 1.1 spec).
In effect: ALL servers return "application/json; charset=utf-8", and not "application/json", because UTF-8 has been the standard for over sixteen years. And: on Wordpress and Github you cannot override this header.
So: it is technically impossible to verify apps if your company happens to run a normal website. 80% of the Internet, which runs on Wordpress and Github, cannot verify an Azure application.
Please, please, please modify the App Registration | Branding | Publisher Domain verification to either (a) accept the specification standard header for JSON, which is and always will be "application/json; charset=utf-8", or (b) allow us to use a DNS CNAME or TXT record validation, like all other verification systems on the Internet (such as Google, AWS, or Oracle).
Thank you,
David Phipps
VP of Engineering
Raydiant, Inc.