langchain/cli/main.py/PlusCommand/start
class PlusCommand:    def start(
        self,
        *,
        expose: bool = False,
        auth_token: Optional[str] = None,
        dev: bool = False,
        openai_api_key: Optional[str] = None,
    ) -> None:
        """Run the LangChainPlus server locally.

        Args:
            expose: If True, expose the server to the internet using ngrok.
            auth_token: The ngrok authtoken to use (visible in the ngrok dashboard).
                If not provided, ngrok server session length will be restricted.
            dev: If True, use the development (rc) image of LangChainPlus.
            openai_api_key: The OpenAI API key to use for LangChainPlus
                If not provided, the OpenAI API Key will be read from the
                OPENAI_API_KEY environment variable. If neither are provided,
                some features of LangChainPlus will not be available.
        """
        if dev:
            os.environ["_LANGCHAINPLUS_IMAGE_PREFIX"] = "rc-"
        if openai_api_key is not None:
            os.environ["OPENAI_API_KEY"] = openai_api_key
        if expose:
            self._start_and_expose(auth_token=auth_token)
        else:
            self._start_local()