That correct I am using the LDAP scheme, and providing it with the appropriate DN string. The only problem is that it allways says authentication failed, without giving any error messages. So I tried with some success to test the LDAP packages provided by oracle.

I am able to authenticate using dbms_ldap, but that only works when I provide NULL for a password.

DECLARE
vSession DBMS_LDAP.session;
vResult PLS_INTEGER;
BEGIN
DBMS_LDAP.use_exception := TRUE;
vSession := DBMS_LDAP.init
( hostname => 'CREDPWY01SDCG01'
, portnum => 389
);
vResult := DBMS_LDAP.simple_bind_s
( ld => vSession
, dn => 'CN=<username>,dc=credit,dc=com'
, passwd => NULL
);
DBMS_Output.put_line('User authenticated!');
vResult := DBMS_LDAP.unbind_s(vSession);
END;

I am not able to authenticate at all when using apex_ldap regardless if I pass NULL for the password, or use the real password.

BEGIN
IF APEX_LDAP.authenticate
( p_username => '<username>'
, p_password => NULL
, p_search_base => 'dc=credit,dc=com'
, p_host => 'CREDPWY01SDCG01'
, p_port => 389
)
THEN
DBMS_Output.put_line('ok');
ELSE
DBMS_Output.put_line('not ok');
END IF;
END;

That did the trick. Instead of using a standard DN string 'cn=%LDAP_USER%, dn=mydomain, dn=com' you just use the following string mydomain\%LDAP_USER%