Fixed.

i use horde3 with imp4 with imap. in horde i use 'basic auth' as 
authentication. My password contains characters which are quoted by 
php. From manual this is the default behavior [1]. But if horde uses 
these credentials for imp to log to an imap-server, the password is 
wrong, because of to much '\'. So i think you have to check with 
get_magic_quotes_gpc(), if an stripslash is necessary or not.

file lib/Horde/Auth/http.php,in function transparent()

my function look like this:
     function transparent()
     {
         if (!empty($_SERVER['PHP_AUTH_USER']) &&
             !empty($_SERVER['PHP_AUTH_PW'])) {

             if (get_magic_quotes_gpc()){
                 $this->setAuth($_SERVER['PHP_AUTH_USER'],
                            array('password' => 
stripslashes($_SERVER['PHP_AUTH_PW']),
                                  'transparent' => 1));
             } else {
                 $this->setAuth($_SERVER['PHP_AUTH_USER'],
                            array('password' => $_SERVER['PHP_AUTH_PW'],
                                  'transparent' => 1));
             }
             return true;
         }

         $this->_setAuthError(AUTH_REASON_MESSAGE, _("HTTP 
Authentication not found."));
         return false;
     }


[1] http://php.speedbone.de/manual/en/function.addslashes.php
  The PHP directive  magic_quotes_gpc is on by default, and it 
essentially runs addslashes() on all GET, POST, and COOKIE data. Do 
not use addslashes() on strings that have already been escaped with 
magic_quotes_gpc as you'll then do double escaping. The function 
get_magic_quotes_gpc() may come in handy for checking this.