Extend rake task to run with cron

lib/tasks/ldap_groups.rake

@@ -31,10 +31,23 @@ namespace :ldap_groups do
   desc 'Synchronize groups and their users from the LDAP auth source.' \
        'Will only synchronize for those users already present in the application.'
   task synchronize: :environment do
-    LdapAuthSource.find_each do |ldap|
-      puts ("-" * 20)
-      puts "Synchronizing for ldap auth source #{ldap.name}"
-      OpenProject::LdapGroups::Synchronization.new(ldap)
+
+    begin
+      LdapAuthSource.find_each do |ldap|
+        puts ("-" * 20)
+        puts "Synchronizing for ldap auth source #{ldap.name}"
+        OpenProject::LdapGroups::Synchronization.new(ldap)
+      end
+    rescue =>  e
+      msg = "Failed to run LDAP group synchronization. #{e.class.name}: #{e.message}"
+      Rails.logger.error msg
+      warn msg
     end
   end
 end
+
+# Ensure core cron task is loaded
+load 'lib/tasks/cron.rake'
+Rake::Task["openproject:cron:hourly"].enhance do
+  Rake::Task["ldap_groups:synchronize"].invoke
+end