def set_credentials(self, username, password=None, region=None,
            tenant_id=None, authenticate=False):
        """
        Sets the username and password directly. Because Rackspace auth uses
        the api_key, make sure that any old values are cleared.
        """
        self.api_key = None
        super(RaxIdentity, self).set_credentials(username, password=password,
                region=region, tenant_id=tenant_id, authenticate=authenticate)
Sets the username and password directly. Because Rackspace auth uses
        the api_key, make sure that any old values are cleared.