Don't change the providername without migrating

config/initializers/1_settings.rb

@@ -62,7 +62,7 @@ if Settings.ldap['enabled'] || Rails.env.test?
   if Settings.ldap['host'].present?
     server = Settings.ldap.except('sync_time')
     server['label'] = 'LDAP'
-    server['provider_id'] = 'main'
+    server['provider_id'] = ''
     Settings.ldap['servers'] = [server]
   end
 

config/initializers/7_omniauth.rb

 module OmniAuth::Strategies
   Gitlab.config.ldap.servers.each_with_index do |server|
+    next unless server.provider_id.present?
     const_set(server.provider_class, Class.new(LDAP))
   end
 end