The OpenID Connect realm enables Elasticsearch to serve as an OpenID Connect Relying Party (RP) and provides single sign-on (SSO) support in Kibana.
It is specifically designed to support authentication via an interactive web browser, so it does not operate as a standard authentication realm. Instead, there are Kibana and Elasticsearch security features that work together to enable interactive OpenID Connect sessions.
This means that the OpenID Connect realm is not suitable for use by standard REST clients. If you configure an OpenID Connect realm for use in Kibana, you should also configure another realm, such as the native realm in your authentication chain.
In order to simplify the process of configuring OpenID Connect authentication within the Elastic Stack, there is a step-by-step guide: Configuring single sign-on to the Elastic Stack using OpenID Connect.