You can integrate Shield with external authentication systems by implementing a custom realm. A custom realm is an Elasticsearch plugin that interacts with an external system to confirm the identity of users trying to access nodes protected by Shield.
Sample code that illustrates the structure and implementation of a custom realm is provided in the shield-custom-realm-example repository. You can use this code as a starting point for creating your own realm.
For more information about creating and using custom realms, see [Integrating with Other Authentication Systems] (https://www.elastic.co/guide/en/shield/2.0.0-beta2/custom-realms.html) in the Shield Reference. For more information about building Elasticsearch Plugins, see [Elasticsearch Plugins and Integrations] (https://www.elastic.co/guide/en/elasticsearch/plugins/2.0/index.html).