Add documentation for hashing passwords

Fixes #7432

Adds HTTP API documentation as well as `rabbitmqctl hash_password` docs.

Add `rabbitmqctl` docs

(cherry picked from commit f420487)
(cherry picked from commit 7efd584)
(cherry picked from commit 1e49ff3)

deps/rabbit/docs/rabbitmqctl.8

@@ -2222,6 +2222,15 @@ The name of the queue to purge.
 .Pp
 Purges a queue (removes all messages in it).
 .El
+.\" ------------------------------------------------------------------
+.It Cm hash_password Ar plaintext
+.Bl -tag -width Ds
+.It Ar plaintext
+The plaintext password to hash
+.El
+.Pp
+Hashes a plaintext password according to the currently configured password hashing algorithm
+.El
 .\" ------------------------------------------------------------------------------------------------
 .Sh PLUGIN COMMANDS
 .\" ------------------------------------------------------------------------------------------------

deps/rabbitmq_cli/lib/rabbitmq/cli/ctl/commands/hash_password_command.ex

@@ -9,7 +9,6 @@ defmodule RabbitMQ.CLI.Ctl.Commands.HashPasswordCommand do
 
   @behaviour RabbitMQ.CLI.CommandBehaviour
   use RabbitMQ.CLI.Core.MergesNoDefaults
-  use RabbitMQ.CLI.DefaultOutput
 
   def run([cleartextpassword], _opts) do
     hash_password(cleartextpassword)
@@ -46,11 +45,16 @@ defmodule RabbitMQ.CLI.Ctl.Commands.HashPasswordCommand do
     :ok
   end
 
+  ## Use default output for all non-special case outputs
+  use RabbitMQ.CLI.DefaultOutput
+
   def usage, do: "hash_password <cleartext_password>"
 
   def banner([arg], _options),
     do: "Will hash password #{arg}"
 
   def banner([], _options),
     do: "Will hash provided password"
+
+  def description(), do: "Hashes a plaintext password"
 end

deps/rabbitmq_management/priv/www/api/index.html

@@ -1157,6 +1157,16 @@ <h2>Reference</h2>
           A list of authentication attempts by remote address and username.
         </td>
       </tr>
+      <tr>
+        <td>X</td>
+        <td></td>
+        <td></td>
+        <td></td>
+        <td class="path">/api/auth/hash_password/<i>plaintext-password</i></td>
+        <td>
+          Hashes <code>plaintext-password</code> according to the currently configured password hashing algorithm.
+        </td>
+      </tr>
     </table>