atlas-pca-fastmcp

FastMCP guard for Proof-Carrying Authority (PCA): make every FastMCP tool call proof-carrying and policy-gated. A tool only runs when the agent carries a valid, in-plan, resource-correct proof for exactly that action. The adapter delegates all verification to atlas-pca and reimplements no cryptography.

Status: 0.4.1, unaudited.

What is tested

The default test suite runs without the framework, against the shared conformance proofs. A second suite, make test-real (needs the framework installed), runs against the real framework and is pinned to FastMCP 4.1.0. It covers a real FastMCP server with the middleware, called through a real in-memory Client: proof in _meta and in tool arguments, absent/undecodable/tampered proofs, wrong audience, insufficient capability, the @pca_tool registry and the policy hook, each asserting the refusal reason the client sees. Each denial test checks that the tool body never ran, and checks the refusal reason wherever the framework surfaces it.

Not covered: other framework versions (only the pinned one is exercised), live model providers (the models are scripted and offline), and any property of the underlying atlas-pca verifier beyond what it already documents. This package has not been independently audited.

Install

pip install atlas-pca-fastmcp

This installs atlas-pca>=0.4.1,<0.5 as a dependency.

Use

Entry points: PCAMiddleware.

from atlas_pca_fastmcp import PCAMiddleware

See the module docstrings in atlas_pca_fastmcp for the full API, and the PCA specification for the model. The verifier applies the full check order, including grant_ref_bound (the signed grant_ref must equal the root capability id), as of atlas-pca 0.2.0.

Links

• Source: https://github.com/Atlas-Authorization/pca-python
• Specification and docs: https://github.com/Atlas-Authorization/pca

License: MIT