How to use voter for request based authorization ?

A custom request based authorization can be useful when we decide if connected user can access to a web page based on 2 criteria:
* the current Request.
* one or more external information (usernames whitelist, IP blacklist, current time...).

Backlog:
* [x] As website owner, homepage should be accessible for everyone (connected and non-connected users)
* [x] As website owner, ONLY connected users being in "private beta authorization list" should be granted to access web app
* [x] As website owner, connected users NOT IN "private beta authorization list" should receive a 403 ACCESS DENIED response.