createUserLinkWithId

Link an external user from a 3rd party identity provider to a FusionAuth user.

SERVERFusionauth SOURCE@fusionauth/mcp-api

Medium RISK CLASS

Category Write

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/io-fusionauth-mcp-api/createuserlinkwithid.md

WHAT IT DOES

What createUserLinkWithId does on Fusionauth

AI agents use createUserLinkWithId to create or update resources in Fusionauth, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Fusionauth environment.

RISK

Why createUserLinkWithId is rated Medium

This tool creates a new link/relationship between two user identities. It is reversible (links can typically be removed), so it falls into the Write category rather than Destructive.

From the tool's definition Tool name and description indicate it 'Link an external user from a 3rd party identity provider to a FusionAuth user' — this creates or establishes a new association between user identities, modifying FusionAuth's user data structure.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs createUserLinkWithId safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Fusionauth, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For createUserLinkWithId, this is the rule to start with:

createUserLinkWithId Rate-limited

createUserLinkWithId 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": {
    "createUserLinkWithId": {
      "limits": [
        {
          "counter": "createuserlinkwithid_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Fusionauth, apply this rule, and every createUserLinkWithId call is checked against it from then on.

FAQ

Questions about createUserLinkWithId

What does the createUserLinkWithId tool do? +

Link an external user from a 3rd party identity provider to a FusionAuth user. It is categorised as a Write tool in the Fusionauth MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on createUserLinkWithId? +

Register the Fusionauth MCP server in PolicyLayer and add a rule for createUserLinkWithId: 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 Fusionauth. Nothing to install.

What risk level is createUserLinkWithId? +

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

Can I rate-limit createUserLinkWithId? +

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

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

createUserLinkWithId is provided by the Fusionauth MCP server (@fusionauth/mcp-api). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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