Using APEX_LDAP.IS_MEMBER With Active Directory

I am trying to using the APEX_LDAP.IS_MEMBER function with active directory.

Using this anonymous block for testing:

DECLARE
    v_username   VARCHAR2 (50) := null;
    v_password   VARCHAR2 (50) := null;
BEGIN
    IF APEX_LDAP.IS_MEMBER (
           p_username     => v_username,
           p_pass         => v_password,
           p_auth_base    => 'user@example.com',
           p_host         => 'dc1.example.com',
           p_port         => 389,
           p_group        => 'ExecutiveDashboard',
           p_group_base   => 'ou=Groups, dc=example, dc=com')
    THEN
        DBMS_OUTPUT.PUT_LINE ('Is allowed to access executive dashboard');
    ELSE
        DBMS_OUTPUT.PUT_LINE ('Is not allowed to access executive dashboard');
    END IF;
END;

What ever user I try with this does not work. What do I need to change to make this work so that it can accurately detect a user that is a member of a particular group?