Many thanks for your prompt response and for pointing me at the appropriate spec, Howard.
I don't believe that chaining and proxies are an option as I have no control over the configuration of the LDAP server and must instead adapt the client to accommodate servers that utilise referrals.
One alternative I've considered is:
1) Disable referral chasing in the client:
ldap_set_option( ld , LDAP_OPT_REFERRALS , LDAP_OPT_OFF );
2) Bind to the top level server using master credentials. 3) Search for the specified user; if the user doesn't exist at that server, one or more referrals will be returned. 4) Iterate over each referral attempting to bind to each one using the user's credentials until either the bind succeeds or I run out of referral candidates.
If you have time to comment on that proposal, I'd be very grateful.
Kind regards, Mike
On Wed, 11 May 2022 at 22:57, Howard Chu hyc@symas.com wrote:
Mike Stevens wrote:
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 http://xxx.com dn: dc=xxx,dc=com description: xxx.com http://xxx.com dc: xxx o: xxx.com http://xxx.com objectClass: top objectClass: dcObject objectClass: organization
# Users, xxx.com http://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%3E*
# mike, Users, xxx.com http://xxx.com dn: uid=mike,ou=Users,dc=xxx,dc=com cn: mike ou: Users uid: mike givenName: Mike mail: mike@uk.xxx.com mailto: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 <
http://serverB.xxx.com:389/dc=uk,dc=xxx,dc=com%3E
The intent is to redirect any requests received by serverA that refer to
the subtree uk.xxx.com http://uk.xxx.com to serverB.
The tree on serverB contains:
# xxx.com http://xxx.com dn: dc=xxx,dc=com description: xxx.com http://xxx.com dc: xxx o: xxx.com http://xxx.com objectClass: top objectClass: dcObject objectClass: organization
# uk.xxx.com http://uk.xxx.com dn: dc=uk,dc=xxx,dc=com dc: uk o: uk.xxx.com http://uk.xxx.com description: xxx Users in the UK objectClass: dcObject objectClass: organization
# mike, uk.xxx.com http://uk.xxx.com dn: uid=mike,dc=uk,dc=xxx,dc=com cn: mike uid: mike givenName: Mike mail: mike@uk.xxx.com mailto: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 <
http://uk.xxx.com%3E, 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 <
http://serverB.xxx.com:389/dc=uk,dc=xxx,dc=com??sub%3E
... 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 mailto: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?
No. See RFC3296 section 5.6.1.
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?
You will need to configure chaining or some other proxy mechanism instead.
Many thanks for your advice, Mike
-- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/