[Openid-specs-authzen] Fwd: [modelcontextprotocol/modelcontextprotocol] Spec Proposal: A Gateway-Based Authorization Model (Discussion #804)

[David Brossard]

Interesting comment re. MCP and authorization

---------- Forwarded message ---------
From: policylayer-dan <notifications at github.com>
Date: Tue, Mar 10, 2026 at 10:52 PM
Subject: Re: [modelcontextprotocol/modelcontextprotocol] Spec Proposal: A
Gateway-Based Authorization Model (Discussion #804)
To: modelcontextprotocol/modelcontextprotocol <
modelcontextprotocol at noreply.github.com>
Cc: David Brossard <david.brossard at gmail.com>, Comment <
comment at noreply.github.com>


Great proposal. We've built a working open-source implementation of this
pattern — Intercept <https://github.com/PolicyLayer/Intercept> is a
transparent MCP proxy that evaluates every tools/call request against
YAML-defined policies before forwarding to the upstream server.

It addresses several of the problems outlined here:

   - *Fine-grained per-request enforcement*: Each tool call is evaluated
   against rules that can check tool name, argument values, and stateful
   counters (rate limits, spend caps). This gives you the "checkpoints for
   each subsequent action" the proposal describes.
   - *No client-side changes*: The agent connects to Intercept like any MCP
   server. It doesn't know the proxy is there.
   - *Deterministic policy*: Rules are YAML, evaluated at the transport
   layer — below the model context. The agent can't reason around them.
   - *Works today*: npx -y @policylayer/intercept -c policy.yaml --
   <server-command> wraps any stdio MCP server.

Would be interested in how the spec could formally accommodate per-request
policy enforcement, whether as part of the gateway model or as a standalone
extension.

https://github.com/PolicyLayer/Intercept

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