OAuth 2.1 for MCP the sequence problem
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Been running MCP in prod for a while now and request-level auth is mostly solved. You scope tokens per server with Resource Indicators and validate audience on every call. What still bugs me is that OAuth can confirm each individual call is authorized but it can't tell you whether the full sequence of tool calls the agent is chaining together is actually legitimate behavior. An agent chaining five legitimate tools in the right order can produce an outcome no one intended to permit.
Put a gateway in front of our MCP servers to evaluate requests with context from what came before. It's more infrastructure than I'd like but nothing else really fits.
Curious how others are handling this, and also how you prevent tokens from leaking into model context.