> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sublay.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Use Sign Testing Jwt

# `useSignTestingJwt`

## Overview

The `useSignTestingJwt` hook is a development-only utility that allows you to sign JSON Web Tokens (JWTs) directly in the client. It is intended for **testing and initial development** when backend infrastructure for signing tokens is not yet in place.

> ⚠️ **Warning:** This method is **insecure for production** use. Exposing your private key in client-side code introduces serious security risks. For production scenarios, JWTs must be signed securely on your backend.

If you are integrating Replyke with your own authentication system, see the section on **Authentication with External User Systems** for guidance on implementing secure token generation.

## Usage Example

```tsx theme={null}
import { useEffect, useState } from "react";
import { useSignTestingJwt } from "@replyke/react-js";

const PROJECT_ID = import.meta.env.VITE_PUBLIC_REPLYKE_PROJECT_ID;
const PRIVATE_KEY = import.meta.env.VITE_PUBLIC_REPLYKE_SECRET_KEY;

function ExampleComponent() {
  const signTestingJwt = useSignTestingJwt();
  const [jwt, setJwt] = useState<string>();

  useEffect(() => {
    const sign = async () => {
      const payload = { id: "user_123", name: "Jane Doe" };

      const token = await signTestingJwt({
        projectId: PROJECT_ID,
        privateKey: PRIVATE_KEY,
        payload,
      });

      setJwt(token);
    };

    sign();
  }, []);

  return <div>JWT: {jwt || "Signing..."}</div>;
}
```

## Parameters & Returns

### Parameters

The `signTestingJwt` function returned by the hook accepts a single object with the following fields:

<ParamField path="projectId" type="string">
  The Replyke project ID for which the JWT is being signed.
</ParamField>

<ParamField path="privateKey" type="string">
  The private key used to sign the JWT. **For development only.**
</ParamField>

<ParamField path="payload" type="Record<string, any>">
  The payload object to include in the signed JWT.
</ParamField>

### Returns

The hook returns an asynchronous function:

<ResponseField name="jwt" type="string">
  The signed JWT as a string. Returns `undefined` if an error occurs.
</ResponseField>