Govern a tool server

You are a platform engineer. You want calls to an MCP server, an HTTP API, or a gRPC service checked by Stratium, whichever agent or client is calling.

Pick the surface by what you are protecting:

You're protecting	Use	How it fits in
An MCP server used by Claude Desktop, ChatGPT desktop, Claude Code, or Codex	mcp	Runs in place of the server's launch command and wraps it. Checks every tools/call.
An HTTP API behind Envoy	extauthz	Envoy asks Stratium about every request before forwarding it.
A gRPC service	proxy	The client points at the proxy instead of the service. No other change.
Something else, from your own Python code	Python SDK	Call Session.check() before each action.

The MCP journey

1. Register the agent and start a session, as in Your first governed agent, with the tools the agent may call.
2. Replace the server's command in the harness's MCP configuration with stratium-pep mcp, and pass the real server in STRATIUM_PEP_MCP_UPSTREAM_COMMAND and STRATIUM_PEP_MCP_UPSTREAM_ARGS.
3. Use the agent normally. Allowed calls pass through to the real server. A refused call never reaches it: the agent gets a JSON-RPC error carrying the reason instead.

The agent still sees the server's full tool list. Stratium checks calls, not the menu, so the agent finds its limits by being refused.

mcp lists every variable, with a worked configuration.

The API and gRPC journey

1. Give the calling client a delegation, with session-start or the Python SDK, granting the requests or methods it may call. For proxy, tool names are full gRPC method paths, such as /orders.v1.Orders/Cancel. Add them to the tool catalog like any other tool.
2. Put the PEP in the path: register extauthz as Envoy's external authorization service, or point the client at proxy. For gRPC, that is the only change on the client side.
3. Have the client attach its token to every request, along with a DPoP proof. These surfaces require sender-constrained tokens, so a stolen token is useless without the client's key. A refused gRPC call returns PermissionDenied with the reason.

Choosing between them

	hook / mcp	extauthz / proxy
Who's calling	a local agent you launched	any client on the network
If the PDP is down	can use a recent cached decision	refuses everything, with no cache
Token	bearer, from the session file	sender-constrained (DPoP)

A PDP outage is an outage of what it guards

extauthz and proxy never fall back to a cache, because on the network the caller is the party being checked. If the PDP is unreachable, every request to the API behind it is refused. Size the PDP's availability to match the API's.

Limits to know

• The catalog decides what Stratium can see. Register each tool the server exposes in the tool catalog, naming the argument that holds the resource, so caps and scopes can apply. Don't guess the field names: capture a real call first, as described in Installing stratium-pep.