Behaviour for login when already logged in is poor

[SysPete]

Code here in post /login route:

Dancer2-Plugin-Auth-Extensible/lib/Dancer2/Plugin/Auth/Extensible.pm

Lines 1057 to 1060 in 37f3fa9

	if ( $plugin->logged_in_user ) {
	$app->redirect( $app->request->params->{return_url}
	|| $plugin->user_home_page );
	}

    if ( $plugin->logged_in_user ) {
        $app->redirect( $app->request->params->{return_url}
              || $plugin->user_home_page );
    }

So if user1 is logged and then user2 tries to login then user1 stays logged in and user gets redirected. I think we should produce some kind of error at the least.