LDAP Authentication Error – ActiveSupport::MessagePack::UnserializableObjectError

Hi everyone,

I’m using the discourse-ldap-auth plugin on a self-hosted Discourse (Docker install).
After a recent rebuild, LDAP authentication started failing for all users.

Here’s the relevant error from production.log:

(ldap) Authentication failure! ldap_error: ActiveSupport::MessagePack::UnserializableObjectError,
Unsupported type Net::BER::BerIdentifiedString for object “******** (Kullanıcı Teknolojileri Yönetim Müdürlüğü)”
Started GET “/auth/failure?message=ldap_error&origin=http%3A%2F%2Fic*ot*rol.va**fb*nk.intra%2Flogin&strategy=ldap”
Processing by Users::OmniauthCallbacksController#failure as HTML
Completed 200 OK

Details

  • The issue affects all LDAP users.

  • All users in our LDAP directory have displayName values containing Turkish characters (ğ, ü, ş, İ, etc.).

  • The error occurs right after the LDAP authentication attempt — no user gets logged in.

Is this a general problem with the latest version of Discourse? Could it be related to a Ruby incompatibility? What solution do you suggest?