Can I get a second opinion on changing this to:

    def __init__(self, url=None, verify_ssl=None, username=None, password=None,
                 client_name=None, client_version=None, app_name=None):
        assert url, "HTTPService requires config to have 'url'"

And now the code is self-documenting.  Since we're already breaking backwards compatibity, the implementatoin change will have to be:

    HTTPService(config)
    
to

    HTTPService(**config)