Additing error details and escape method to nodes_dn #7681 (#7703)

* Additing error details and escape method to nodes_dn #7681

Signed-off-by: AntonEliatra <[email protected]>

* Update security-settings.md

Signed-off-by: AntonEliatra <[email protected]>

* Apply suggestions from code review

Signed-off-by: Naarcha-AWS <[email protected]>

---------

Signed-off-by: AntonEliatra <[email protected]>
Signed-off-by: Naarcha-AWS <[email protected]>
Co-authored-by: Naarcha-AWS <[email protected]>
(cherry picked from commit 506b101)
Signed-off-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

_install-and-configure/configuring-opensearch/security-settings.md

@@ -15,7 +15,7 @@ The following sections describe security-related settings in `opensearch.yml`. T
 
 The Security plugin supports the following common settings:
 
--  `plugins.security.nodes_dn` (Static): Specifies a list of distinguished names (DNs) that denote the other nodes in the cluster. This setting supports wildcards and regular expressions. The list of DNs are also read from the security index **in addition** to the YAML configuration when `plugins.security.nodes_dn_dynamic_config_enabled` is `true`.
+-  `plugins.security.nodes_dn` (Static): Specifies a list of distinguished names (DNs) that denote the other nodes in the cluster. This setting supports wildcards and regular expressions. The list of DNs are also read from the security index **in addition** to the YAML configuration when `plugins.security.nodes_dn_dynamic_config_enabled` is `true`. If this setting is not configured correctly, the cluster will fail to form as the nodes will not be able to trust each other and will result in the following error: `Transport client authentication no longer supported`.
 
 - `plugins.security.nodes_dn_dynamic_config_enabled` (Static): Relevant for `cross_cluster` use cases where there is a need to manage the  allow listed `nodes_dn` without having to restart the nodes every time a new `cross_cluster` remote is configured.
   Setting `nodes_dn_dynamic_config_enabled` to `true` enables **super-admin callable** Distinguished Names APIs, which provide means to update or retrieve `nodes_dn` dynamically. This setting only has effect if `plugins.security.cert.intercluster_request_evaluator_class` is not set. Default is `false`.
@@ -357,6 +357,7 @@ The Security plugin supports the following transport layer security settings:
 plugins.security.nodes_dn:
   - "CN=*.example.com, OU=SSL, O=Test, L=Test, C=DE"
   - "CN=node.other.com, OU=SSL, O=Test, L=Test, C=DE"
+  - "CN=node.example.com, OU=SSL\, Inc., L=Test, C=DE" # escape additional comma with `\`
 plugins.security.authcz.admin_dn:
   - CN=kirk,OU=client,O=client,L=test, C=de
 plugins.security.roles_mapping_resolution: MAPPING_ONLY