Can a Bind result in a Referral?

Good day.

I’m an LDAP novice and am attempting to modify an LDAP client to accommodate an LDAP server environment that makes use of referrals.

I have installed openLDAP 2.4.44 on 2 RHEL 7.9 servers.

The initial entries in the tree on serverA contains :

# xxx.com dn: dc=xxx,dc=com description: xxx.com dc: xxx o: xxx.com objectClass: top objectClass: dcObject objectClass: organization

# Users, xxx.com dn: ou=Users,dc=xxx,dc=com ou: Users description: xxx Users objectClass: organizationalUnit

# search reference *ref: ldap://serverB.xxx.com:389/dc=uk,dc=xxx,dc=com??sub http://serverB.xxx.com:389/dc=uk,dc=xxx,dc=com??sub*

# mike, Users, xxx.com dn: uid=mike,ou=Users,dc=xxx,dc=com cn: mike ou: Users uid: mike givenName: Mike mail: mike@uk.xxx.com objectClass: Person objectClass: organizationalPerson objectClass: inetOrgPerson

I believe the "ref" entry is known as a subordinate referral;

it was created by populating the tree from an LDIF file that contained the following:

dn: dc=uk,dc=xxx,dc=com objectClass: referral objectClass: extensibleObject dc: uk ref: ldap://serverB.xxx.com:389/dc=uk,dc=xxx,dc=com

The intent is to redirect any requests received by serverA that refer to the subtree uk.xxx.com to serverB.

The tree on serverB contains:

# xxx.com dn: dc=xxx,dc=com description: xxx.com dc: xxx o: xxx.com objectClass: top objectClass: dcObject objectClass: organization

# uk.xxx.com dn: dc=uk,dc=xxx,dc=com dc: uk o: uk.xxx.com description: xxx Users in the UK objectClass: dcObject objectClass: organization

# mike, uk.xxx.com dn: uid=mike,dc=uk,dc=xxx,dc=com cn: mike uid: mike givenName: Mike mail: mike@uk.xxx.com objectClass: person objectClass: organizationalPerson objectClass: inetOrgPerson

Now, if I perform a search on serverA specifying a base of uk.xxx.com, I get an RC=10 Referral result as expected:

[root@serverA ~]# ldapsearch -x '(uid=mike)' -b dc=uk,dc=xxx,dc=com -LL version: 1

Referral (10) Matched DN: dc=uk,dc=xxx,dc=com Referral: ldap://serverB.xxx.com:389/dc=uk,dc=xxx,dc=com??sub

... and I can chase that referral using the -C option to retrieve the entry from serverB:

[root@Mike21 ~]# ldapsearch -x '(uid=mike)' -b dc=uk,dc=ibm,dc=com -LL -C version: 1

dn: uid=mike,dc=uk,dc=xxx,dc=com cn: mike uid: mike givenName: Mike mail: mike@uk.xxx.com objectClass: person objectClass: organizationalPerson objectClass: inetOrgPerson

But, if I attempt a bind to serverA using the user that exists in serverB, I get an authentication failure:

[root@serverA ~]# ldapsearch -x -b 'dc=uk,dc=xxx,dc=com' -D uid=mike,dc=uk,dc=xxx,dc=com -w passw0rD ldap_bind: Invalid credentials (49)

Now, I realise that the failure would be expected as the bind DN doesn't exist at serverA. But I read that every request apart from unbind and abandon can result in a referral. So why doesn't the bind follow the "ref" to serverB? Is that possible and have I not configured my server correctly?

Ultimately, what I'd like to do in my client is something like:

ld_user = ldap_init( "ldap://serverA:389/dc=uk,dc=xxx,dc=com" , 0 );

... followed by :

err = ldap_simple_bind_s( ld_user, "uid=mike,dc=uk,dc=xxx,dc=com" , password);

... and have LDAP authenticate the given user against serverB based on the referral in serverA.

Is this sort of set up possible?

Many thanks for your advice, Mike