backport ms graph plugin docs to 8.19

Author: richard-dennehy

docs/plugins/authentication.asciidoc

@@ -0,0 +1,10 @@
+[[authentication]]
+= Authentication Plugins
+
+Authentication plugins extend the functionality provided by the built-in {ref}/realms.html
+
+[discrete]
+==== Core authentication plugins
+
+<<ms-graph-authz,Microsoft Graph Authz>>::
+The Microsoft Graph Authz plugin uses https://learn.microsoft.com/en-us/graph/api/user-list-memberof/[Microsoft Graph] to look up group membership information from Microsoft Entra ID

docs/plugins/images/01-create-enterprise-application.png

@@ -47,6 +47,8 @@ include::repository.asciidoc[]
 
 include::store.asciidoc[]
 
+include::authentication.asciidoc[]
+
 include::integrations.asciidoc[]
 
 include::authors.asciidoc[]

docs/plugins/images/02-find-app-registration.png

@@ -0,0 +1,97 @@
+[[ms-graph-authz]]
+=== Microsoft Graph Authz
+
+The Microsoft Graph Authz plugin uses [Microsoft Graph](https://learn.microsoft.com/en-us/graph/api/user-list-memberof) to look up group membership information from Microsoft Entra ID.
+
+This is primarily intended to work around the Microsoft Entra ID maximum group size limit (see [Group overages](https://learn.microsoft.com/en-us/security/zero-trust/develop/configure-tokens-group-claims-app-roles#group-overages)).
+
+:plugin_name: microsoft-graph-authz
+include::install_remove.asciidoc[]
+
+[[configure-azure]]
+==== Configure Azure
+
+To make API calls to Microsoft Graph, Elasticsearch requires Azure credentials with the correct permissions.
+
+=== Create a custom Azure Application
+
+. Log in to the https://portal.azure.com[Azure portal] and go to Microsoft Entra ID
+. Click "Enterprise applications" and then "New application" to register a new application.
+. Click "Create your own application", provide a name, and select the "Integrate any other application you don’t find in the gallery" option.
+
+image::images/01-create-enterprise-application.png["create your own application" page]
+
+=== Configure the custom Application
+
+. In the [Azure portal](https://portal.azure.com), go to Microsoft Entra ID.
+. Under “App registrations”, then the “All applications” tab, find the application created in the previous section.
+
+image::images/02-find-app-registration.png[find your app registration]
+. Take note of the Application (client) ID and Tenant ID shown here - these will be needed to configure Elasticsearch later.
+
+image::images/03-get-application-id.png[get your application ID]
+. Under Manage > Certificates & secrets
+   - Create a new client secret
+   - Take note of the Value - this is needed later, and is only shown once
+
+image::images/04-create-client-secret.png[get your client secret]
+. Under Manage > API permissions
+   - Go to “Add a permission”
+   - Choose “Microsoft Graph”
+   - Choose “Application permissions”
+   - Select “Directory.ReadWrite.All, Group.ReadWrite.All, User.Read.All”
+   - Note that an Azure Admin will need to approve these permissions before the credentials can be used
+
+image::images/05-configure-api-permissions.png[configure api permissions]
+
+[[configuration-properties]]
+==== Configuration properties
+
+Once the plugin is installed, the following configuration settings are available:
+
+xpack.security.authc.realms.microsoft_graph.*.order::
+    The priority of the realm within the realm chain. Realms with a lower order are consulted first. The value must be unique for each realm. This setting is required.
+
+xpack.security.authc.realms.microsoft_graph.*.tenant_id::
+    Your Microsoft Entra ID [Tenant ID](https://learn.microsoft.com/en-us/entra/fundamentals/how-to-find-tenant). This setting is required.
+
+xpack.security.authc.realms.microsoft_graph.*.client_id::
+    The Application ID of the Enterprise Application you registered in the previous section. This setting is required.
+
+xpack.security.authc.realms.microsoft_graph.*.client_secret::
+    The client secret value for the Application you registered in the previous section. This is a sensitive setting, and must be configured in the Elasticsearch keystore. This setting is required.
+
+xpack.security.authc.realms.microsoft_graph.*.access_token_host::
+    A Microsoft login URL. Defaults to `https://login.microsoftonline.com`.
+
+xpack.security.authc.realms.microsoft_graph.*.graph_host::
+    The Microsoft Graph base address. Defaults to `https://graph.microsoft.com/v1.0`.
+
+xpack.security.authc.realms.microsoft_graph.*.http_request_timeout::
+    The timeout for individual Graph HTTP requests. Defaults to `10s`.
+
+xpack.security.authc.realms.microsoft_graph.*.execution_timeout::
+    The overall timeout for authorization requests to this plugin. Defaults to `30s`.
+
+Create a Microsoft Graph realm, following the above settings, then configure an existing realm to delegate to it using `authorization_realms`.
+
+For example, to authenticate via Microsoft Entra with SAML and use the Microsoft Graph plugin to look up group membership:
+
+[source,yaml]
+----
+xpack.security.authc.realms.saml.kibana-realm:
+  order: 2
+  attributes.principal: nameid
+  attributes.groups: "http://schemas.microsoft.com/ws/2008/06/identity/claims/groups"
+  idp.metadata.path: "https://login.microsoftonline.com/<Tenant ID>/federationmetadata/2007-06/federationmetadata.xml?appid=<Application_ID>"
+  idp.entity_id: "https://sts.windows.net/<Tenant_ID>/"
+  sp.entity_id: "<Kibana_Endpoint_URL>"
+  sp.acs: "<Kibana_Endpoint_URL>/api/security/saml/callback"
+  sp.logout: "<Kibana_Endpoint_URL>/logout"
+  authorization_realms: microsoft_graph1
+
+xpack.security.authc.realms.microsoft_graph.microsoft_graph1:
+  order: 3
+  tenant_id: "<Tenant_ID>"
+  client_id: "<Graph_Application_ID>"
+----