Add ansible-vault encrypt_string doc (#24147)

* Add documentation on 'ansible-vault encrypt_string'

docs/docsite/rst/playbooks_vault.rst

@@ -136,7 +136,26 @@ As of version 2.3, Ansible can now use a vaulted variable that lives in an other
     other_plain_text: othervalue
 
 
-This vaulted variable be decrypted with the supplied vault secret and used as a normal variable. The `ansible-vault` command line supports stdin and stdout for encrypting data on the fly, which can be used from your favorite editor to create these vaulted variables; you just have to be sure to add the `!vault` tag so both Ansible and YAML are aware of the need to decrypt. The `|` is also required, as vault encryption results in a multi-line string.
+This vaulted variable be decrypted with the supplied vault secret and used as a normal variable. The `ansible-vault` command line supports `STDIN` and `STDOUT` for encrypting data on the fly, which can be used from your favorite editor to create these vaulted variables; you just have to be sure to add the `!vault` tag so both Ansible and YAML are aware of the need to decrypt. The `|` is also required, as vault encryption results in a multi-line string. The leading spaces will be ignored and some indentation is required for it to be valid YAML.
+
+As of version 2.3, one way to generate the inline secret is to use `ansible-vault encrypt_string` which will output the secret to `STDOUT`::
+
+   $ ansible-vault encrypt_string "42"
+   !vault-encrypted |
+          $ANSIBLE_VAULT;1.1;AES256
+          <vault cipher text here>
+
+   $ ansible-vault encrypt_string "42" --stdin-name "the_answer"
+    the_answer: !vault-encrypted |
+          $ANSIBLE_VAULT;1.1;AES256
+          <vault cipher text here>
+
+   $ echo -n "the plaintext to encrypt" | ansible-vault encrypt_string
+   !vault-encrypted |
+          $ANSIBLE_VAULT;1.1;AES256
+          <vault cipher text here>
+
+Note the use of `echo -n`. If you use just `echo` the encrypted string will have a new line (`\n`) on the end.
 
 
 .. _speeding_up_vault:

docs/man/man1/ansible-vault.1.asciidoc.in

@@ -12,7 +12,7 @@ ansible-vault - manage encrypted ansible vars files (YAML).
 
 SYNOPSIS
 --------
-ansible-vault [create|decrypt|edit|encrypt|rekey] [--help] [options] file_name
+ansible-vault [create|decrypt|edit|encrypt|encrypt_string|rekey] [--help] [options] file_name
 
 
 DESCRIPTION
@@ -116,6 +116,24 @@ Thus any of the following invocations can be used:
 Reading from stdin and writing only encrypted output is a good way to prevent
 sensitive data from ever hitting disk (either interactively or from a script).
 
+
+ENCRYPT_STRING
+--------------
+
+*$ ansible-vault encrypt_string [options] "string cheese"*
+
+The *encrypt_string* sub-command is used to encrypt a string supplied as an argument.
+
+The *encrypt_string* command works with *STDIN* and has the additional options
+*--name* and *--stdin-name*:
+
+*$ ansible-vault encrypt_string "munster" -name="cheese_du_jour"*
+*$ ansible-vault encrypt_string "$@" -stdin-name="cheese_list" < ./cheese_list.txt*
+
+The output will be on *STDOUT*. This command is useful for creating inline
+secrets introduced in version 2.3.
+
+
 DECRYPT
 -------