it works if you put it on:
imp/config/hooks.php

'appauthenticated' ('appinitialized' in H4).

Hello,
right guess. I am using imp for authentication.
So you are saying that postauthenticate is only executed after 
successful horde auth? This is sad and not clearly documented.
Do i have another way to "post authenticate"? I want to doublecheck 
against an ldap after successful imp (does make sense in my special 
case)

Can't reproduce.  Are you actually using horde for authentication (as 
opposed to imp)?

Hello,
The postauthenticate hook seems to be not executed. Minimal example:

<HORDE/config/hooks.php>
public function postauthenticate($userId, $credentials)
{
     return false;
}

As always: Thx