https://support.apple.com/guide/security/recoveryos-and-diag...
> When the internet recovery and diagnostic modes were added to Mac computers in 2011, it was decided that it would be better to use the simpler HTTP transport, and handle content authentication using the chunklist mechanism, rather than implement the more complicated HTTPS functionality in the UEFI firmware, and thus increase the firmwareʼs attack surface.
¹https://github.com/acidanthera/OpenCorePkg/blob/4a740c3f256e...
[edit] Added macrecovery.py info
Now, apparently this uses plain http - but if tls/https is an option - any client (like curl/wget) should by definition come with a ssl trust root (os or bundled). If this is mitm'ed, you've got big problems. Certificate pinning doesn't really help that much in this case.