The authority exists, the manufactures. The whole purpose of secure boot is to stop untrusted code running. If something the manufactures sign can run third par

The authority exists, the manufactures. The whole purpose of secure boot is to stop untrusted code running. If something the manufactures sign can run third party code, then it can be used to run untrusted code. This means they will either never make such a key, or revoke it when they do sign it. This simply means, with its current design, linux is incompatible with secure boot.