This tracks exactly with why I built MCP Gateway — the root causes you listed (absent authentication, blind trust, no access control) are all things the protocol leaves up to each implementer to solve independently.

https://github.com/PanosSalt/MCP-Gateway

OAuth 2.1 + PKCE, Microsoft Entra SSO, per-tool RBAC, full audit trail on every tool call. The gateway sits in front of your tools so auth and access control are solved once at the platform level rather than per-server. Self-hostable with Docker.

First open source project — built it after seeing exactly the pattern described here in enterprise MCP deployments.