auth0 multiple clients architecture

I use auth0 as my auth2 provider. Let's assume I have 4 web application under the same company.

Do I have to authorize the user with auth0 from each web server, or to build one server that is used as the security middleware, that will get calls from all the web apps with the user token, and it will check it with the auth0 provider, and return true/flase?

Thanks.