Authentication type for MCP connections: - none: No authentication - headers: Static header-based authentication (admin sets API keys / custom headers once, shared by all callers) - oauth: OAuth 2.0 authentication (server-level, admin authenticates once) - per_user_oauth: Per-user OAuth 2.0 authentication (each user authenticates individually) - per_user_headers: Per-user headers (each user submits their own header values; admin declares the schema)