Just leak them to the inference providers, obviously /s

If you have self hosted models and/or self hosted APIs, maybe you don’t need MCP to provide a gateway to a secure resource.

If neither of those things are true, you need an authenticating gateway/proxy or a target API that supports single use credentials (and get the model to generate a call to use them).

We can argue whether MCP is a good authenticating middle layer, but not whether one is required.