$userdata
$userdata :
Userdata array
Just a reference to $_SESSION, for BC purposes.
CodeIgniter Session Class
_configure_sid_length() : void
Configure session ID length
To make life easier, we used to force SHA-1 and 4 bits per character on everyone. And of course, someone was unhappy.
Then PHP 7.1 broke backwards-compatibility because ext/session is such a mess that nobody wants to touch it with a pole stick, and the one guy who does, nobody has the energy to argue with.
So we were forced to make changes, and OF COURSE something was going to break and now we have this pile of shit. -- Narf