STEP_USER_DATA_SCHEMA = vol.Schema(
    {
        vol.Optional(CONF_NAME, DEFAULT_NAME): str,
        vol.Required(CONF_API_KEY): str,
        vol.Required(CONF_API_SECRET): str,
        vol.Required(CONF_DOMAIN, DEFAULT_DOMAIN): str,
    }
)

...

async def async_step_user(self, user_input):
    """Handle the initial step."""
    if user_input is None:
        return self.async_show_form(
            step_id="user", data_schema=STEP_USER_DATA_SCHEMA
        )

...