Add connection info module

To extract client ID at authentication time.

[#166271318]

References #1767

deps/rabbitmq_web_mqtt/src/rabbit_web_mqtt_connection_info.erl

@@ -0,0 +1,34 @@
+%% The contents of this file are subject to the Mozilla Public License
+%% Version 1.1 (the "License"); you may not use this file except in
+%% compliance with the License. You may obtain a copy of the License
+%% at https://www.mozilla.org/MPL/
+%%
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and
+%% limitations under the License.
+%%
+%% The Original Code is RabbitMQ.
+%%
+%% The Initial Developer of the Original Code is GoPivotal, Inc.
+%% Copyright (c) 2019 Pivotal Software, Inc.  All rights reserved.
+%%
+-module(rabbit_web_mqtt_connection_info).
+
+%% Module to add the MQTT client ID to authentication properties
+
+%% API
+-export([additional_authn_params/4]).
+
+additional_authn_params(_Creds, _VHost, _Pid, Infos) ->
+    case proplists:get_value(variable_map, Infos, undefined) of
+        VariableMap when is_map(VariableMap) ->
+            case maps:get(<<"client_id">>, VariableMap, []) of
+                ClientId when is_binary(ClientId)->
+                    [{client_id, ClientId}];
+                [] ->
+                    []
+            end;
+        _ ->
+            []
+    end.