bash: base64url encode and decode

base64url.sh

# base64url encode
function base64url_encode {
  (if [ -z "$1" ]; then cat -; else echo -n "$1"; fi) |
    openssl base64 -e -A |
      sed s/\\+/-/g |
      sed s/\\//_/g |
      sed -E s/=+$//
}

# base64url decode
function base64url_decode {
  INPUT=$(if [ -z "$1" ]; then echo -n $(cat -); else echo -n "$1"; fi)
  MOD=$(($(echo -n "$INPUT" | wc -c) % 4))
  PADDING=$(if [ $MOD -eq 2 ]; then echo -n '=='; elif [ $MOD -eq 3 ]; then echo -n '=' ; fi)
  echo -n "$INPUT$PADDING" |
    sed s/-/+/g |
    sed s/_/\\//g |
    openssl base64 -d -A
}

can you help me please
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