fetch_s3

fetch_s3_file() {
  local bucket=$1
  local file_path=$2
  local iam_policy=$3

  local metadata_path="169.254.169.254/latest/meta-data/iam/security-credentials"

  CREDENTIALS=$(curl http://$metadata_path/$iam_policy/)
  key_id=$(echo $CREDENTIALS | jq '.AccessKeyId' | sed 's/"//g')
  key_secret=$(echo $CREDENTIALS | jq '.SecretAccessKey' | sed 's/"//g')
  session_token=$(echo $CREDENTIALS | jq '.Token' | sed 's/"//g')

  date="$(LC_ALL=C date -u +"%a, %d %b %Y %X %z")"
  sig="$(printf "GET\n\n\n$date\n/$bucket/$file_path" | openssl sha1 -binary -hmac "$key_secret" | base64)"

  curl -XGET https://s3.amazonaws.com/$file_path \
    -O \
    -H "Date: ${date}" \
    -H "x-amz-security-token: $session_token" \
    -H "Authorization: AWS $key_id:$sig"
}