I also have a small guide on how to enroll Haiku’s keys into your BIOS to use EFI Secure Boot.
https://cgit.haiku-os.org/haiku/tree/data/boot/efi/keys/README.md
We sign our release bootloaders with our own cert, so you have to add the Haiku, Inc. cert into your BIOS as a trusted vendor.
Keep in mind, there really isn’t a benefit since our bootloader doesn’t cryptographically check our kernel. All your doing is ensuring Haiku’s bootloader hasn’t been tampered with.