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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _generate_auth_token(self, channel_name):
 """Generate a token for authentication with the given channel. :param str channel_name: Name of the channel to generate a signature for. :rtype: str """

        subject = "{}:{}".format(self.connection.socket_id, channel_name)
        h = hmac.new(self.secret_as_bytes, subject.encode('utf-8'), hashlib.sha256)
        auth_key = "{}:{}".format(self.key, h.hexdigest())

        return auth_key