Custom handler for /client initConnect requests

I want to ask if anyone knows more about this?
It’s listed under Advanced Setups in the proxy page.

Implementing a custom handler for /client initConnect requests and delegating a successful connection to the actual backend server’s initConnect sequence. This could be used for a server picker or some other creative things.

I’m interested in the server picker part of that message but I can’t find any information about this anywhere.
It’s the only part of the proxy setup documentation that I actually have no clue on how to properly implement.

curl -X POST -d “method=initConnect&name=FakePlayerName&guid=FakeGuid&protocol=12&gameBuild=2802&gameName=gta5&cfxTicket=YourTicket” http://localhost:30120/client

This is as far as I got now (just testing on terminal), I’m reading the source and see if I understand how it works, now I need to get a guid and ticket, ticket should be more trivial (or i’ll just set lan param), but guid not sure yet.
I’m not sure yet how a server picker would be made from this ?
I’ll have to try more