How to install, initialize and use auth0.js v9
https://auth0.com/docs/libraries/auth0js/v9#initialization
* here
* example directory
* node
* methods of installation
* how to initialize auth0.js
* signup
* login
* logout
* Client Settings
* npm
* yarn
* Hosted Login Page
* /authorize endpoint
* cross-origin authentication
* cross-origin authentication
* universal login
* universal login
* third-party applications
* Dashboard
* Linking Accounts
* User Metadata
* Linking Accounts