IoT Hub MQTT Paho issues

By examining source code of azure-iot-cli-extension I came up with this:

def generate_sas_token(uri, key, policy=None, expiry=3600, absolute=False):
    """
    Create a shared access signature token as a string literal.
    Args:
        uri (str): Uri of target resource.
        policy (str): Name of shared access policy.
        key (str): Shared access key.
        expiry (int): Future expiry (in seconds) of the token to be generated.
        absolute (bool): In general the sas token ttl is generated relative to 'now' (UTC) + expiry.
            Set to true to generate a sas token with no relative start.
    Returns:
        result (str): SAS token as string literal.
    """
    encoded_uri = quote_plus(uri)
    ttl = int(expiry) if absolute else int(time() + expiry)
    sign_key = '%s\n%d' % (encoded_uri, ttl)
    signature = b64encode(HMAC(b64decode(key), sign_key.encode('utf-8'), sha256).digest())

    result = {
        'sr': uri,
        'sig': signature,
        'se': str(ttl)
    }

    if policy:
        result['skn'] = policy

    return 'SharedAccessSignature ' + urlencode(result)

Still, I cant connect one publisher and one subscriber at the same time, so major question still remains.