feat: add Step-Up Authentication section and related examples to documentation

[gyaneshgouraw-okta]

Summary

Add step-up authentication support via popup for the refresh token flow. When getAccessTokenSilently encounters an mfa_required error, the SDK can now automatically open a Universal Login popup for the user to complete MFA, then return the token transparently — no custom MFA UI required.

Changes

• Export PopupOpenError and the InteractiveErrorHandler type from the public API, enabling consumers to handle popup errors and type the new configuration option
• Add documentation and usage examples for step-up authentication via the interactiveErrorHandler: "popup" provider option, including setup, usage, and error handling

Example

<Auth0Provider
  domain="YOUR_AUTH0_DOMAIN"
  clientId="YOUR_AUTH0_CLIENT_ID"
  authorizationParams={{
    redirect_uri: window.location.origin,
    audience: 'https://api.example.com/',
  }}
  useRefreshTokens={true}
  interactiveErrorHandler="popup"
>
  <MyApp />
</Auth0Provider>

Once configured, getAccessTokenSilently handles MFA challenges automatically:

const token = await getAccessTokenSilently({
  authorizationParams: { audience: 'https://api.example.com/', scope: 'read:sensitive' },
});

Testing

• Verified InteractiveErrorHandler property behaviour via a step up flow