set_credentials · Fastly NGWAF MCP Server MCP: Risk & Policy

WHAT IT DOES

What set_credentials does on Fastly NGWAF MCP Server

AI agents use set_credentials to create or update resources in Fastly NGWAF MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Fastly NGWAF MCP Server environment.

WHY IT NEEDS A POLICY

Why set_credentials needs a policy

This tool writes/stores sensitive authentication credentials. While not destructive (credentials can be overwritten), and not immediately financial, it is a Write operation with high severity because: (1) compromised credentials grant access to the Fastly NGWAF API and all sibling tools (create/delete rules, sites, analytics), (2) an AI agent setting incorrect or attacker-controlled credentials could redirect all…

From the tool's definition Tool directly modifies stored credentials by setting email and access token. The description explicitly states 'Set Fastly NGWAF API credentials', which is a write operation that creates or updates authentication material.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

set_credentials Rate-limited

set_credentials 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.

View as policy code

policy.json

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

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Fastly NGWAF MCP Server, so you can run agents against it safely.

FAQ

Questions about set_credentials

What does the set_credentials tool do? +

Set Fastly NGWAF API credentials (email and access token). It is categorised as a Write tool in the Fastly NGWAF MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on set_credentials? +

Register the Fastly NGWAF MCP Server MCP server in PolicyLayer and add a rule for set_credentials: 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 Fastly NGWAF MCP Server. Nothing to install.

What risk level is set_credentials? +

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

Can I rate-limit set_credentials? +

Yes. Add a rate_limit block to the set_credentials 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 set_credentials completely? +

Set action: deny in the PolicyLayer policy for set_credentials. 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 set_credentials? +

set_credentials is provided by the Fastly NGWAF MCP Server MCP server (purpleax/fastlymcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.