BerriAI/litellm · error · ValueError

Invalid config for MCP server '{server_name or server_id}':

Error message

Invalid config for MCP server '{server_name or server_id}': auth_type oauth2 requires an explicit oauth2_flow (got {config_oauth2_flow!r}). Set oauth2_flow: client_credentials for machine-to-machine servers (the proxy mints a shared token at token_url using client_id/client_secret, no user interaction) or oauth2_flow: authorization_code for interactive servers (per-user tokens via browser sign-in, including delegate_auth_to_upstream).

What it means

Error "Invalid config for MCP server '{server_name or server_id}': auth_type oauth2 requires an explicit oauth2_flow (got {config_oauth2_flow!r}). Set oauth2_flow: client_credentials for machine-to-machine servers (the proxy mints a shared token at token_url using client_id/client_secret, no user interaction) or oauth2_flow: authorization_code for interactive servers (per-user tokens via browser sign-in, including delegate_auth_to_upstream)." thrown in BerriAI/litellm.

Source

Thrown at litellm/proxy/_experimental/mcp_server/mcp_server_manager.py:1705

            resolved_authorization_url = manual_authorization_url or (
                gated_oauth_metadata.authorization_url if gated_oauth_metadata else None
            )
            resolved_token_url = manual_token_url or (gated_oauth_metadata.token_url if gated_oauth_metadata else None)
            resolved_registration_url = manual_registration_url or (
                gated_oauth_metadata.registration_url if gated_oauth_metadata else None
            )
            discovered_issuer = (
                gated_oauth_metadata.discovered_issuer
                if gated_oauth_metadata and not gated_oauth_metadata.from_origin_fallback
                else None
            )
            effective_issuer = manual_issuer or discovered_issuer

            if auth_type == MCPAuth.oauth2 and config_oauth2_flow not in (
                "client_credentials",
                "authorization_code",
            ):
                raise ValueError(
                    f"Invalid config for MCP server '{server_name or server_id}': auth_type oauth2 "
                    f"requires an explicit oauth2_flow (got {config_oauth2_flow!r}). Set "
                    "oauth2_flow: client_credentials for machine-to-machine servers (the proxy mints "
                    "a shared token at token_url using client_id/client_secret, no user interaction) "
                    "or oauth2_flow: authorization_code for interactive servers (per-user tokens via "
                    "browser sign-in, including delegate_auth_to_upstream)."
                )

            config_dcr_bridge = server_config.get("dcr_bridge", None)
            if config_dcr_bridge is not None and not isinstance(config_dcr_bridge, bool):
                raise ValueError(
                    f"Invalid config for MCP server '{server_name or server_id}': dcr_bridge "
                    f"must be a boolean (got {config_dcr_bridge!r})."
                )
            if config_dcr_bridge and auth_type not in (
                MCPAuth.true_passthrough,
                MCPAuth.oauth_delegate,
            ):

View on GitHub (pinned to 77b7c6c40c)

Solutions

1. Set oauth2_flow to client_credentials (machine-to-machine) or authorization_code (interactive) in the server config.

Example fix

oauth2_flow: client_credentials

When it happens

Trigger: Thrown at litellm/proxy/_experimental/mcp_server/mcp_server_manager.py:1705 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/380958368cfebcdc. Report an issue: GitHub.