sapl-fastmcp

Policy-based authorization for FastMCP servers. Write access control rules as external SAPL policy files and enforce them at runtime through middleware or per-component auth= callbacks. Policies can be updated without code changes or redeployment.

Built on sapl-base and the SAPL 4.1 enforcement model: planner-driven constraint handling, the SUSPEND decision verb, and an optional RSocket transport.

How It Works

Two enforcement approaches are available. The middleware approach intercepts every tool call, resource read, and prompt get through SAPLMiddleware, giving you a single enforcement point for the entire server. The per-component approach uses auth=sapl() on individual tools, resources, and prompts for fine-grained control with decorator overrides.

Middleware

from fastmcp import FastMCP
from sapl_base.transport import HttpPdpClientOptions
from sapl_fastmcp import SAPLMiddleware, configure_sapl, get_pdp_client, get_planner

configure_sapl(HttpPdpClientOptions(base_url="https://localhost:8443"))
mcp = FastMCP("my-server")
mcp.add_middleware(SAPLMiddleware(get_pdp_client(), get_planner()))

Per-Component Auth

from fastmcp import FastMCP
from sapl_base.transport import HttpPdpClientOptions
from sapl_fastmcp import sapl, pre_enforce, configure_sapl

configure_sapl(HttpPdpClientOptions(base_url="https://localhost:8443"))
mcp = FastMCP("my-server")

@mcp.tool(auth=sapl())
@pre_enforce(action="query", resource="patients")
def query_patients(department: str) -> list[dict]:
    return [{"id": "P-001", "name": "Jane Doe"}]

If the PDP permits, the tool runs. If not, access is denied. If the decision carries obligations (like access logging or result filtering), they are enforced automatically through registered constraint handlers.

Getting Started

pip install sapl-fastmcp

For setup instructions, configuration options, and the constraint handler reference, see the FastMCP documentation.

Links

• Full Documentation
• FastMCP Integration
• Demo Application
• Report an Issue

License

Apache-2.0