#!/bin/bash

#run as root
#$1 is username
for i in $(awk '{print $2}' "/home/${1}/.ssh/authorized_keys"); do
  dude="$(base64 -d <<< "${i}" | sha256sum | awk '{print $1}' | xxd -r -p | base64)"
  for j in $(grep "Accepted publickey for ${1}" /var/log/auth.log | grep -o "SHA256.*$" | sed 's/^SHA256://g' | sort | uniq); do
    [ "${dude:0:-1}" = "${j}" ] && {
      _users="$(grep "${i}" /home/${1}/.ssh/authorized_keys | awk '{print $3" logged in"}')"
      lastlog_time="$(tac /var/log/auth.log | grep -m1 "${j}" | awk '{print $1" "$2" "$3" "}')"
      echo "${lastlog_time} ${_users}"
    }
  done
done