Convert OpenSSH authorized_keys entries in to sha256 sums used in /var/log/auth.log

authkeys_to_sha256.sh

#! /bin/bash -ex
while read p; do
    echo -e "\n$p ->"
    echo $p | awk '{ print $2 }' | # Only the actual key data without prefix or comments
              base64 -d          | # decode as base64
              sha256sum          | # SHA256 hash (returns hex)
              awk '{ print $1 }' | # only the hex data
              xxd -r -p          | # hex to bytes
              base64               # encode as base64
done < /root/.ssh/authorized_keys

# thanks to https://serverfault.com/a/888300