Add support to define module instead of path to script

src/ejabberd_captcha.erl

@@ -398,6 +398,18 @@ create_image(Limiter, Key) ->
 				   {error, image_error()}.
 do_create_image(Key) ->
     FileName = get_prog_name(),
+    case length(string:split(FileName, "/")) == 1 of
+        true ->
+            do_create_image(Key, misc:binary_to_atom(FileName));
+        false ->
+            do_create_image(Key, FileName)
+    end.
+
+do_create_image(Key, Module) when is_atom(Module) ->
+    Function = create_image,
+    erlang:apply(Module, Function, [Key]);
+
+do_create_image(Key, FileName) when is_binary(FileName) ->
     Cmd = lists:flatten(io_lib:format("~ts ~ts", [FileName, Key])),
     case cmd(Cmd) of
       {ok,
@@ -551,6 +563,7 @@ return(Port, TRef, Result) ->
 is_feature_available() ->
     case get_prog_name() of
       Prog when is_binary(Prog) -> true;
+      MF when is_list(MF) -> true;
       false -> false
     end.
 

src/ejabberd_options_doc.erl

@@ -454,13 +454,14 @@ doc() ->
              ?T("For server connections, this 'ca_file' option is overridden by the http://../toplevel/#s2s-cafile[s2s_cafile] option."), ""
             ]}},
      {captcha_cmd,
-      #{value => ?T("Path"),
+      #{value => ?T("Path | ModuleName"),
-        note => "improved in 21.10",
+        note => "improved in 23.xx",
         desc =>
             ?T("Full path to a script that generates http://../basic/#captcha[CAPTCHA] images. "
                "@VERSION@ is replaced with ejabberd version number in XX.YY format. "
                "@SEMVER@ is replaced with ejabberd version number in semver format "
                "when compiled with Elixir's mix, or XX.YY format otherwise. "
+               "Alternatively, it can be the name of a module that implements ejabberd CAPTCHA support. "
                "There is no default value: when this option is not "
                "set, CAPTCHA functionality is completely disabled."),
         example =>