APEX

Since I linked our Microsoft Active Directory with my Apex application using LDAP, I am trying to retrieve the groups for the user currently logged in from the Active Directory.
Here's the documentation: https://docs.oracle.com/cd/E59726_01/doc.50/e39149/apex_ldap.htm#AEAPI242
Here's my code of my dynamic action on page load, I am trying to retrieve a VARCHAR2 of all the groups the current user is part of, and to put it in a display-only field :

BEGIN
    :P1_NEW := APEX_LDAP.MEMBER_OF2(
        p_username => v('APP_USER'),
        p_pass => 'mypassword',
        p_auth_base => 'DOMAIN\',
        p_host => 'XX.X.XXX.XX',
        p_port => 389);
END;

But when I load my page, this error occurs
Ajax call returned server error ORA-31202: DBMS_LDAP : Erreur client/serveur LDAP : Invalid credentials. 80090308: LdapErr: DSID-0C090439, comment: AcceptSecurityContext error, data 52e, v4563 for Execute PL/SQL Code.
What's wrong in my code ? Thank you in advance for your help.
Thomas