How to load authorized ssh public key from Raspberry Pi 4B bootloader

import-ssh-public-key-from-eeprom

#!/bin/bash

# Include this in the image at /usr/lib/systemd/system-generators/

key=/sys/bus/nvmem/devices/rmem1/nvmem
normal_dir=$1
[ -e $key ] || exit 0

n_reverse=$(od -An -N256 -vtx1 -w1 $key | tr -d '\n ')
for (( i=0; i<512; i=i+2 )) ; do n="${n_reverse:$i:2}$n" ; done
e=$(od -An -j256 -N8 -vtx8 --endian=little $key | tr -d '\n ' | sed ':a;s/^00//;ta')

ssh_hex() {
  for str in "$@" ; do
    [ $(( 0x${str:0:1} & 0x8 )) == 0 ] || str="00$str"
    printf "%08X%s" $(( ${#str}/2 )) "${str^^}"
  done
}

mkdir -p $normal_dir/systemd-tmpfiles-setup.service.d

printf '[Service]\nSetCredential=ssh.authorized_keys.root:ssh-rsa %s\\n\n' $(ssh_hex "7373682D727361" "$e" "$n" | basenc --base16 -i -d | basenc --base64 -w0) > $normal_dir/systemd-tmpfiles-setup.service.d/authorized-keys-from-eeprom.conf