Python:如何使用自定义策略cloudfront生成签名URL

import datetime
import hashlib
import hmac
import urllib.parse

def generate_signed_url(url, key_pair_id, private_key_path, expires):
    # 读取私钥文件
    with open(private_key_path, 'r') as f:
        private_key = f.read()

    # 构建待签名的URL
    parsed_url = urllib.parse.urlparse(url)
    resource_path = parsed_url.path if parsed_url.path else '/'
    expires = int(datetime.datetime.now().timestamp()) + expires
    to_sign = f'{resource_path}?Expires={expires}'

    # 使用私钥对待签名的URL进行签名
    signature = hmac.new(private_key.encode('utf-8'), to_sign.encode('utf-8'), hashlib.sha1).digest()
    signature = urllib.parse.quote_plus(signature)

    # 构建最终的签名URL
    signed_url = f'{url}?Expires={expires}&Signature={signature}&Key-Pair-Id={key_pair_id}'

    return signed_url

url = 'https://example.com/image.jpg'  # 要生成签名URL的资源URL
key_pair_id = 'YOUR_KEY_PAIR_ID'  # CloudFront Key Pair的ID
private_key_path = '/path/to/private_key.pem'  # CloudFront Key Pair的私钥文件路径
expires = 3600  # URL的有效期，单位为秒

signed_url = generate_signed_url(url, key_pair_id, private_key_path, expires)
print(signed_url)