feat: add client prop and createAuth0Client factory

[yogeshchoudhary147]

What

Adds two new exports to address the pain point of accessing Auth0 from code that has no access to React's lifecycle (e.g. TanStack Start client function middleware).

• createAuth0Client(options) — a factory that creates an Auth0Client with the auth0-react telemetry header pre-configured. This is the recommended way to create a client when you need to share it outside of React.
• client prop on Auth0Provider — accepts a pre-configured Auth0Client instance instead of creating one internally. When client is provided, domain and clientId become optional.

Closes #1037. Supersedes #849 (thanks to @rodrigowbazevedo for the original draft).

Usage

import { createAuth0Client, Auth0Provider } from '@auth0/auth0-react';

// Create once — use anywhere
const client = createAuth0Client({ domain, clientId });

// Outside React (e.g. TanStack Start client function middleware)
// Note: the raw Auth0Client method is getTokenSilently (not getAccessTokenSilently)
const token = await client.getTokenSilently();

// Inside React — Auth0Provider uses the same client instance
function App() {
  return <Auth0Provider client={client}><MyApp /></Auth0Provider>;
}

Notes

• Fully backward compatible — existing usage without client prop is unchanged
• createAuth0Client is preferred over new Auth0Client() directly as it injects the correct SDK telemetry header
• Auth0Client is also now exported from this package for cases where users manage the client themselves

[rodrigowbazevedo]

Thanks! 🚀

[roccomaniscalco]

Awesome 💯 Thank you!

[rodrigowbazevedo]

This interceptor example is beautiful 🚀