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

authkeys_to_sha256.sh

#!/bin/bash
set -eu -o pipefail

function main() {
  AUTHORIZED_KEYS=${1:-~/.ssh/authorized_keys}
  while read -r p; do
    echo -e "\n$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 $1 }' | # only the hex data
                xxd -r -p          | # hex to bytes
                base64               # encode as base64
  done <<< "$(grep -v '^#' "$AUTHORIZED_KEYS")"
}

main "$@"

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