[imp] problem with composite auth driver (newbie)

[Claude Pomalo]

hello

I have setup a wekk ago a horde groupware with imp/mimp app cheking a
remote pop3 server.

i want that user access the imp/mimp with only one auth login but the
access to horde groupware require sql driver.

i have set this line in my horde/config/conf.php
---------------------------------------------------------
$conf['auth']['params']['drivers']['mysql']['driver'] = 'sql';
$conf['auth']['params']['drivers']['mysql']['params'] = array(
    'driverconfig' => 'horde',
    'encryption' => 'md5-hex',
    'show_encryption' => false);
$conf['auth']['params']['drivers']['imp']['driver'] = 'application';
$conf['auth']['params']['drivers']['imp']['params'] = array(
    'app' => 'imp');
$conf['auth']['params']['drivers']['mimp']['driver'] = 'application';
$conf['auth']['params']['drivers']['mimp']['params'] = array(
    'app' => 'mimp');

$conf['auth']['params']['loginscreen_switch'] =
'_horde_select_loginscreen';
if (!function_exists('_horde_select_loginscreen')) {
    function _horde_select_loginscreen() {
	$url = $_SERVER['REQUEST_URI'];
	if (strpos($url,'imp')!=false) {
	    require_once('Horde/Browser.php');
	    $browser = new Browser();
    	    if ($browser->isMobile()) {
        	return 'mimp';
	    }
	    else {
		return 'imp';
	    }
	}
	else {
	    return 'mysql';
	}
    }
}
--------------------------------------------------------

if i set only the "mysql" driver, i can log in horde but when i add the
imp and mimp drivers, i cannot acces my groupware  and i have always the
horde login screen also for imp and mimp

what's wrong? please

Many thank for your help
claude