The Elastic Stack security features support user authentication using SAML single sign-on (SSO). The security features provide this support using the Web Browser SSO profile of the SAML 2.0 protocol.
This protocol 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 SAML sessions.
This means that the SAML realm is not suitable for use by standard REST clients. If you configure a SAML 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 SAML authentication within the Elastic Stack, there is a step-by-step guide to Configuring SAML single-sign-on on the Elastic Stack.