curl get file from private s3 with iam role

get_s3_file.sh

#!/bin/bash
# https://gist.github.com/afunsten
# https://gist.github.com/davidejones/d05f51df75e659111227

#example: bash get_s3_file.sh -b some-bucket-name -f some-file-key-path -o some-output-file
#you must first give root user of the aws acct bucket access 
#you must also give user role bucket access

while getopts :b:f:o:r: option; do
    case "${option}" in
    	b) bucket="${OPTARG}";;
        f) filekey="${OPTARG}";;
        o) outputfullpath="${OPTARG}";;
        r) region="${OPTARG}";;
    esac
done

#defaults
: "${bucket:=some-bucket-default}"
: "${filekey:=some-file-key-path-default}"
: "${outputfullpath:=./get_s3_file_output}"
: "${region:=}"

instance_profile=`curl -s http://169.254.169.254/latest/meta-data/iam/security-credentials/`
aws_access_key_id=`curl -s http://169.254.169.254/latest/meta-data/iam/security-credentials/${instance_profile} | grep AccessKeyId | cut -d':' -f2 | sed 's/[^0-9A-Z]*//g'`
aws_secret_access_key=`curl -s http://169.254.169.254/latest/meta-data/iam/security-credentials/${instance_profile} | grep SecretAccessKey | cut -d':' -f2 | sed 's/[^0-9A-Za-z/+=]*//g'`
token=`curl -s http://169.254.169.254/latest/meta-data/iam/security-credentials/${instance_profile} | sed -n '/Token/{p;}' | cut -f4 -d'"'`

date="`date +'%a, %d %b %Y %H:%M:%S %z'`"
resource="/${bucket}/${filekey}"
signature_string="GET\n\n\n${date}\nx-amz-security-token:${token}\n/${resource}"
signature=`/bin/echo -en "${signature_string}" | openssl sha1 -hmac ${aws_secret_access_key} -binary | base64`
authorization="AWS ${aws_access_key_id}:${signature}"

curl -s -H "Date: ${date}" -H "X-AMZ-Security-Token: ${token}" -H "Authorization: ${authorization}" "https://s3${region}.amazonaws.com/${resource}" -o "${outputfullpath}"
# for encrpted files  you also need ...
# -H "x-amz-server-side​-encryption​-customer-algorithm: AES256" 
# -H "x-amz-server-side​-encryption​-customer-key: yourstring"
# -H "x-amz-server-side​-encryption​-customer-key-MD5: yourstring" 
#https://docs.aws.amazon.com/AmazonS3/latest/API/RESTObjectGET.html

policy-for-bucket

{
	"Version": "2012-10-17",
	"Id": "Policy1441048292119",
	"Statement": [
		{
			"Sid": "Stmt1441048289544",
			"Effect": "Allow",
			"Principal": {
				"AWS": [
					"arn:aws:iam::123456789012:role/your_role_name",
				]
			},
			"Action": "s3:*",
			"Resource": "arn:aws:s3:::some-bucket-of-mine/*"
		}
	]
}

policy-for-iam

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "s3:*",
            "Resource": [
                "arn:aws:s3:::some-bucket-of-mine",
                "arn:aws:s3:::some-bucket-of-mine/*"
            ]
        },
    ]
}