@staticmethod
    def _url_base64_encode(msg):
        msg_base64 = base64.b64encode(msg)
        msg_base64 = msg_base64.replace('+', '-')
        msg_base64 = msg_base64.replace('=', '_')
        msg_base64 = msg_base64.replace('/', '~')
        return msg_base64
Base64 encodes a string using the URL-safe characters specified by
dataset/ETHPy150Open darcyliu/storyboard/boto/cloudfront/distribution.py/Distribution._url_base64_encode