langchain-ai/langgraph · error · ValueError

Authentication handler already set as {self._authenticate_ha

Error message

Authentication handler already set as {self._authenticate_handler}.

What it means

Error "Authentication handler already set as {self._authenticate_handler}." thrown in langchain-ai/langgraph.

Source

Thrown at libs/sdk-py/langgraph_sdk/auth/__init__.py:297

            ```python
            @auth.authenticate
            async def authenticate(
                method: str,
                path: str,
                headers: dict[str, bytes]
            ) -> Auth.types.MinimalUserDict:
                permissions, user = await verify_request(method, path, headers)
                # Permissions could be things like ["runs:read", "runs:write", "threads:read", "threads:write"]
                return {
                    "identity": user["id"],
                    "permissions": permissions,
                    "display_name": user["name"],
                }
            ```
        """
        if self._authenticate_handler is not None:
            raise ValueError(
                f"Authentication handler already set as {self._authenticate_handler}."
            )
        self._authenticate_handler = fn
        return fn


## Helper types & utilities

V = typing.TypeVar("V", contravariant=True)


class _ActionHandler(typing.Protocol[V]):
    async def __call__(
        self, *, ctx: types.AuthContext, value: V
    ) -> types.HandlerResult: ...


T = typing.TypeVar("T", covariant=True)

View on GitHub (pinned to 38031739e5)

When it happens

Trigger: Thrown at libs/sdk-py/langgraph_sdk/auth/__init__.py:297 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

• Authentication and authorization failures — expired tokens, bad credentials, and missing scopes.

AI-assisted analysis of langchain-ai/langgraph@38031739e5 (2026-08-26). Data as JSON: /api/errors/923735bd097648b2. Report an issue: GitHub.