Merge branch 'backport-ee-2405' into 'master'

Backport "Automatically link Kerberos users and LDAP people" changes to CE

See merge request !12807

lib/gitlab/o_auth/user.rb

@@ -101,14 +101,18 @@ module Gitlab
         # Look for a corresponding person with same uid in any of the configured LDAP providers
         Gitlab::LDAP::Config.providers.each do |provider|
           adapter = Gitlab::LDAP::Adapter.new(provider)
-          @ldap_person = Gitlab::LDAP::Person.find_by_uid(auth_hash.uid, adapter)
-          # The `uid` might actually be a DN. Try it next.
-          @ldap_person ||= Gitlab::LDAP::Person.find_by_dn(auth_hash.uid, adapter)
+          @ldap_person = find_ldap_person(auth_hash, adapter)
           break if @ldap_person
         end
         @ldap_person
       end
 
+      def find_ldap_person(auth_hash, adapter)
+        by_uid = Gitlab::LDAP::Person.find_by_uid(auth_hash.uid, adapter)
+        # The `uid` might actually be a DN. Try it next.
+        by_uid || Gitlab::LDAP::Person.find_by_dn(auth_hash.uid, adapter)
+      end
+
       def ldap_config
         Gitlab::LDAP::Config.new(ldap_person.provider) if ldap_person
       end