DOCS-10018: CLI auth in OpenLDAP Tutorial

Author: nlarew

source/includes/steps-configure-ldap-mongodb.yaml

@@ -75,8 +75,18 @@ title: Authenticate the user in the ``mongo`` shell.
 stepnum: 3
 ref: ldap-sasl-authenticate
 pre: |
-  To perform the authentication in the :program:`mongo` shell, use the
-  :method:`db.auth()` method in the ``$external`` database.
+  To authenticate when connecting with the ``mongo`` shell, run
+  :program:`mongo` with the following options, substituting ``<host>``
+  and ``<user>``, and enter your password when prompted:
+
+  .. class:: copyable-code
+  .. code-block:: shell
+
+     mongo --host <host> --authenticationMechanism PLAIN --authenticationDatabase '$external' -u <user> -p
+
+  Alternatively, connect without supplying credentials and call the
+  :method:`db.auth()` method on the ``$external`` database.
+
 action:
   pre: |
     Specify the value ``"PLAIN"`` in the ``mechanism`` field, the user and