acme-challenge.sh

#!/usr/bin/env bash

keyauth="string-from-acme-client"

_sed() {
  if [[ "${OSTYPE}" = "Linux" ]]; then
    sed -r "${@}"
  else
    sed -E "${@}"
  fi
}

urlbase64() {
  # urlbase64: base64 encoded string with '+' replaced with '-' and '/' replaced with '_'
  openssl base64 -e | tr -d '\n\r' | _sed -e 's:=*$::g' -e 'y:+/:-_:'
}

keyauth_hook="$(printf '%s' "${keyauth}" | openssl dgst -sha256 -binary | urlbase64)"

echo $keyauth_hook