BerriAI/litellm · error · ValueError

OAuth2 token response for MCP server '{server.server_id}' re

Error message

OAuth2 token response for MCP server '{server.server_id}' returned non-object JSON (got {type(body).__name__})

What it means

The client-credentials token endpoint returned 2xx but response.json() parsed to a non-dict (list, string, number). It is a malformed-upstream-response type check; the cached-token path refuses to index into it and raises instead.

Source

Thrown at litellm/proxy/_experimental/mcp_server/oauth2_token_cache.py:160

        verbose_logger.debug(
            "Fetching OAuth2 client_credentials token for MCP server %s",
            server.server_id,
        )

        try:
            response: Final = await client.post(server.token_url, data=data, headers=token_request.headers or None)
            response.raise_for_status()
        except httpx.HTTPStatusError as exc:
            raise ValueError(
                f"OAuth2 token request for MCP server '{server.server_id}' "
                f"failed with status {exc.response.status_code}"
            ) from exc

        body: Final = response.json()

        if not isinstance(body, dict):
            raise ValueError(
                f"OAuth2 token response for MCP server '{server.server_id}' "
                f"returned non-object JSON (got {type(body).__name__})"
            )

        access_token: Final = body.get("access_token")
        if not access_token:
            raise ValueError(f"OAuth2 token response for MCP server '{server.server_id}' missing 'access_token'")

        # Safely parse expires_in — providers may return null or non-numeric values
        raw_expires_in: Final = body.get("expires_in")
        try:
            expires_in = int(raw_expires_in) if raw_expires_in is not None else MCP_OAUTH2_TOKEN_CACHE_DEFAULT_TTL
        except (TypeError, ValueError):
            expires_in = MCP_OAUTH2_TOKEN_CACHE_DEFAULT_TTL

        ttl: Final = max(
            expires_in - MCP_OAUTH2_TOKEN_EXPIRY_BUFFER_SECONDS,
            MCP_OAUTH2_TOKEN_CACHE_MIN_TTL,

View on GitHub (pinned to 77b7c6c40c)

Solutions

1. Check the upstream token endpoint; it must return a JSON object.
2. Log the raw response to diagnose.

Example fix

Inspect token endpoint response body.

When it happens

Trigger: Thrown at litellm/proxy/_experimental/mcp_server/oauth2_token_cache.py:160 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of BerriAI/litellm@77b7c6c40c (2026-08-18). Data as JSON: /api/errors/64ecb6ac52bd4b2d. Report an issue: GitHub.