loginWithId

Authenticates a user to FusionAuth. This API optionally requires an API key. See <code>Application.loginConfiguration.requireAuthentication</code>.

SERVERFusionauth SOURCE@fusionauth/mcp-api

High RISK CLASS

Category Execute

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/loginwithid.md

WHAT IT DOES

What loginWithId does on Fusionauth

AI agents invoke loginWithId to trigger actions in Fusionauth. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.

RISK

Why loginWithId is rated High

Authenticating a user is not a simple read or write; it executes an authentication flow that produces tokens, sessions, and audit events in FusionAuth. Misuse could allow an AI agent to authenticate as arbitrary users, potentially bypassing access controls. The optional API key requirement lowers the barrier for misuse in some configurations.

From the tool's definition 'Authenticates a user to FusionAuth' — triggers an external authentication operation with session/token side effects

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs loginWithId 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 loginWithId, this is the rule to start with:

loginWithId Rate-limited

loginWithId stays usable, but rate-capped: a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "loginWithId": {
      "limits": [
        {
          "counter": "loginwithid_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL → Instant setup, no code required.

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

FAQ

Questions about loginWithId

What does the loginWithId tool do? +

Authenticates a user to FusionAuth. This API optionally requires an API key. See <code>Application.loginConfiguration.requireAuthentication</code>. It is categorised as a Execute tool in the Fusionauth MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on loginWithId? +

Register the Fusionauth MCP server in PolicyLayer and add a rule for loginWithId: 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 loginWithId? +

loginWithId is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit loginWithId? +

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

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

loginWithId 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.

KEEP EXPLORING

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