Custom Authentication and Access Control for LangGraph Platform

LangGraph now supports custom authentication and resource-level access control for Python deployments, allowing integration with custom auth providers. This feature enables developers to implement granular access patterns, such as scoping conversations to specific users or adding role-based access control. The system uses an `Auth` object with an `@auth.authenticate` handler to validate credentials and `@auth.on` handlers to control access to resources like threads and assistants. By adding metadata to resources and applying filters, developers can build more secure, production-ready applications with fine-grained permissions.