generate_cloudfront_signed_cookies.py

#!/usr/bin/env python """ Copyright (C) 2017 Matt Sullivan Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. Creates and signs cookies that provide access to CloudFront objects Based on: https://aws.amazon.com/premiumsupport/knowledge-center/cf-signed-cookies-s3-origin/ requirements: >=Python3.5 cryptography>=1.7.1 """ import time import json import base64 from cryptography.hazmat.backends import default_backend from cryptography.hazmat.primitives import hashes from cryptography.hazmat.primitives import serialization from cryptography.hazmat.primitives.asymmetric import padding def _replace_unsupported_chars(some_str): """Replace unsupported chars: '+=/' with '-_~'""" return some_str.replace("+", "-") \ .replace("=", "_") \ .replace("/", "~") def _in_an_hour(): """Returns a UTC POSIX timestamp for one hour in the future""" return int(time.time()) + (60*60) def rsa_signer(message, key): """ Based on https://boto3.readthedocs.io/en/latest/reference/services/cloudfront.html#examples """ private_key = serialization.load_pem_private_key( key, password=None, backend=default_backend() ) signer = private_key.signer(padding.PKCS1v15(), hashes.SHA1()) signer.update(message) return signer.finalize() def generate_policy_cookie(url): """Returns a tuple: (policy json, policy base64)""" policy_dict = { "Statement": [ { "Resource": url, "Condition": { "DateLessThan": { "AWS:EpochTime": _in_an_hour() } } } ] } # Using separators=(',', ':') removes seperator whitespace policy_json = json.dumps(policy_dict, separators=(",", ":")) policy_64 = str(base64.b64encode(policy_json.encode("utf-8")), "utf-8") policy_64 = _replace_unsupported_chars(policy_64) return policy_json, policy_64 def generate_signature(policy, key): """Creates a signature for the policy from the key, returning a string""" sig_bytes = rsa_signer(policy.encode("utf-8"), key) sig_64 = _replace_unsupported_chars(str(base64.b64encode(sig_bytes), "utf-8")) return sig_64 def generate_cookies(policy, signature, cloudfront_id): """Returns a dictionary for cookie values in the form 'COOKIE NAME': 'COOKIE VALUE'""" return { "CloudFront-Policy": policy, "CloudFront-Signature": signature, "CloudFront-Key-Pair-Id": cloudfront_id } def generate_curl_cmd(url, cookies): """Generates a cURL command (use for testing)""" curl_cmd = "curl -v" for k, v in cookies.items(): curl_cmd += " -H 'Cookie: {}={}'".format(k, v) curl_cmd += " {}".format(url) return curl_cmd def generate_signed_cookies(url, cloudfront_id, key): policy_json, policy_64 = generate_policy_cookie(url) signature = generate_signature(policy_json, key) return generate_cookies(policy_64, signature, cloudfront_id) if __name__ == "__main__": import argparse # Parse the command line args parser = argparse.ArgumentParser(description="Generates signed cookies for Amazon CloudFront") parser.add_argument("url", type=str, help="URL to sign") parser.add_argument("key", type=str, help="private key to use to sign the cookie") parser.add_argument("id", type=str, help="CloudFront id") args = parser.parse_args() with open(args.key, "rb") as f: cookies = generate_signed_cookies(args.url, args.id, f.read()) print(generate_curl_cmd(args.url, cookies))