[DOCS] Add security section to Elasticsearch book (#46883)

Co-Authored-By: Tim Vernum <tim@adjective.org>

docs/reference/index.asciidoc

@@ -18,8 +18,6 @@ include::setup.asciidoc[]
 
 include::monitoring/configuring-monitoring.asciidoc[]
 
-include::{xes-repo-dir}/security/configuring-es.asciidoc[]
-
 include::setup/bootstrap-checks-xes.asciidoc[]
 
 include::upgrade.asciidoc[]
@@ -54,6 +52,8 @@ include::frozen-indices.asciidoc[]
 
 include::high-availability.asciidoc[]
 
+include::security/index.asciidoc[]
+
 include::commands/index.asciidoc[]
 
 include::how-to.asciidoc[]

docs/reference/security/index.asciidoc

@@ -0,0 +1,18 @@
+[[secure-cluster]]
+= Secure a cluster
+
+[partintro]
+--
+The {stack-security-features} enable you to easily secure a cluster. You can
+password-protect your data as well as implement more advanced security
+measures such as encrypting communications, role-based access control,
+IP filtering, and auditing.
+
+* <<elasticsearch-security>>
+* <<configuring-security>>
+
+--
+
+include::overview.asciidoc[]
+
+include::{xes-repo-dir}/security/configuring-es.asciidoc[]

docs/reference/security/overview.asciidoc

@@ -0,0 +1,63 @@
+[role="xpack"]
+[[elasticsearch-security]]
+== Security overview
+++++
+<titleabbrev>Overview</titleabbrev>
+++++
+
+Security protects {es} clusters by:
+
+* <<preventing-unauthorized-access, Preventing unauthorized access>>
+  with password protection, role-based access control, and IP filtering.
+* <<preserving-data-integrity, Preserving the integrity of your data>>
+  with SSL/TLS encryption.
+* <<maintaining-audit-trail, Maintaining an audit trail>>
+  so you know who's doing what to your cluster and the data it stores.
+
+[float]
+[[preventing-unauthorized-access]]
+=== Preventing unauthorized access
+
+To prevent unauthorized access to your {es} cluster, you must have a
+way to _authenticate_ users. This simply means that you need a way to validate
+that a user is who they claim to be. For example, you have to make sure only
+the person named _Kelsey Andorra_ can sign in as the user `kandorra`. The
+{es-security-features} provide a standalone authentication mechanism that enables
+you to quickly password-protect your cluster. If you're already using LDAP, 
+Active Directory, or PKI to manage users in your organization, the
+{security-features} are able to integrate with those systems to perform user
+authentication.
+
+In many cases, simply authenticating users isn't enough. You also need a way to
+control what data users have access to and what tasks they can perform. The
+{es-security-features} enable you to _authorize_ users by assigning access
+_privileges_ to _roles_ and assigning those roles to users. For example, this
+role-based access control mechanism (a.k.a RBAC) enables you to specify that the
+user `kandorra` can only perform read operations on the `events` index and can't
+do anything at all with other indices.
+
+The {security-features} also support IP-based authorization.
+You can whitelist and blacklist specific IP addresses or subnets to control
+network-level access to a server.
+
+[float]
+[[preserving-data-integrity]]
+=== Preserving data integrity
+
+A critical part of security is keeping confidential data confidential.
+{es} has built-in protections against accidental data loss and
+corruption. However, there's nothing to stop deliberate tampering or data
+interception. The {stack-security-features} preserve the integrity of your
+data by encrypting communications to and from nodes. For even	
+greater protection, you can increase the <<ciphers,encryption strength>>.
+
+[float]
+[[maintaining-audit-trail]]
+=== Maintaining an audit trail
+
+Keeping a system secure takes vigilance. By using {stack-security-features} to
+maintain an audit trail, you can easily see who is accessing your cluster and
+what they're doing. By analyzing access patterns and failed attempts to access
+your cluster, you can gain insights into attempted attacks and data breaches.
+Keeping an auditable log of the activity in your cluster can also help diagnose
+operational issues.