link_session_to_user

THE RISK

Medium Risk

Why link_session_to_user needs a policy

This tool writes data to Sift (a fraud detection platform) by linking a session to a user account. While it creates a data association rather than directly moving money, it operates within a payment protocol server (AP2) and modifies trust/fraud detection state.

From the tool's definition Tool sends a $link_session_to_user event to Sift, which creates or modifies a session-to-user association in an external fraud detection/analytics service. The verb 'send' and 'event' indicate a write operation that creates/updates state.

Documented attack patterns abuse exactly the kind of access link_session_to_user gives an agent:

POLICY

How to control link_session_to_user

PolicyLayer is an MCP gateway — it sits between your AI agents and Mcp Ap2, and nothing reaches the server without passing your rules. This is the rule we recommend for link_session_to_user:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "link_session_to_user": {
      "limits": [
        {
          "counter": "link_session_to_user_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

link_session_to_user stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

Create a free account and register Mcp Ap2 — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Mcp Ap2 tools

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All 1300 Mcp Ap2 tools →

Write tools on other servers

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Argument validation → Checking tool call arguments against schema and policy before they run.
Scoped token → Per-person credentials that grant a defined subset of servers and tools.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about link_session_to_user

What does the link_session_to_user tool do? +

Send a $link_session_to_user event to Sift. It is categorised as a Write tool in the Mcp Ap2 MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on link_session_to_user? +

Register the Mcp Ap2 MCP server in PolicyLayer and add a rule for link_session_to_user: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Mcp Ap2. Nothing to install.

What risk level is link_session_to_user? +

link_session_to_user is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit link_session_to_user? +

Yes. Add a rate_limit block to the link_session_to_user rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block link_session_to_user completely? +

Set action: deny in the PolicyLayer policy for link_session_to_user. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides link_session_to_user? +

link_session_to_user is provided by the Mcp Ap2 MCP server (@codespar/mcp-ap2). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Mcp Ap2 tool call.

Start from Mcp Ap2, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →