diff --git a/apps/emqx_message_transformation/src/emqx_message_transformation.erl b/apps/emqx_message_transformation/src/emqx_message_transformation.erl
index cff7e3133..94951ff4f 100644
--- a/apps/emqx_message_transformation/src/emqx_message_transformation.erl
+++ b/apps/emqx_message_transformation/src/emqx_message_transformation.erl
@@ -3,6 +3,8 @@
 %%--------------------------------------------------------------------
 -module(emqx_message_transformation).
 
+-feature(maybe_expr, enable).
+
 -include_lib("snabbkaffe/include/trace.hrl").
 -include_lib("emqx_utils/include/emqx_message.hrl").
 -include_lib("emqx/include/emqx_hooks.hrl").
@@ -54,11 +56,18 @@
 
 -type eval_context() :: #{
     client_attrs := map(),
+    clientid := _,
+    flags := _,
+    id := _,
+    node := _,
     payload := _,
+    peername := _,
+    publish_received_at := _,
     qos := _,
     retain := _,
     topic := _,
     user_property := _,
+    username := _,
     dirty := #{
         payload => true,
         qos => true,
@@ -323,20 +332,35 @@ message_to_context(#message{} = Message, Payload, Transformation) ->
             true -> #{};
             false -> #{payload => true}
         end,
-    UserProperties0 = maps:get(
-        'User-Property',
-        emqx_message:get_header(properties, Message, #{}),
-        []
-    ),
+    Flags = emqx_message:get_flags(Message),
+    Props = emqx_message:get_header(properties, Message, #{}),
+    UserProperties0 = maps:get('User-Property', Props, []),
     UserProperties = maps:from_list(UserProperties0),
+    Headers = Message#message.headers,
+    Peername =
+        case maps:get(peername, Headers, undefined) of
+            Peername0 when is_tuple(Peername0) ->
+                iolist_to_binary(emqx_utils:ntoa(Peername0));
+            _ ->
+                undefined
+        end,
+    Username = maps:get(username, Headers, undefined),
     #{
         dirty => Dirty,
+
         client_attrs => emqx_message:get_header(client_attrs, Message, #{}),
+        clientid => Message#message.from,
+        flags => Flags,
+        id => emqx_guid:to_hexstr(Message#message.id),
+        node => node(),
         payload => Payload,
+        peername => Peername,
+        publish_received_at => Message#message.timestamp,
         qos => Message#message.qos,
         retain => emqx_message:get_flag(retain, Message, false),
         topic => Message#message.topic,
-        user_property => UserProperties
+        user_property => UserProperties,
+        username => Username
     }.
 
 -spec context_to_message(emqx_types:message(), eval_context(), transformation()) ->
diff --git a/apps/emqx_message_transformation/test/emqx_message_transformation_http_api_SUITE.erl b/apps/emqx_message_transformation/test/emqx_message_transformation_http_api_SUITE.erl
index 9728ca71d..fa83c8024 100644
--- a/apps/emqx_message_transformation/test/emqx_message_transformation_http_api_SUITE.erl
+++ b/apps/emqx_message_transformation/test/emqx_message_transformation_http_api_SUITE.erl
@@ -285,14 +285,17 @@ connect(ClientId, IsPersistent) ->
     connect(ClientId, IsPersistent, _Opts = #{}).
 
 connect(ClientId, IsPersistent, Opts) ->
+    StartProps = maps:get(start_props, Opts, #{}),
     Properties0 = maps:get(properties, Opts, #{}),
     Properties = emqx_utils_maps:put_if(Properties0, 'Session-Expiry-Interval', 30, IsPersistent),
-    {ok, Client} = emqtt:start_link([
-        {clean_start, true},
-        {clientid, ClientId},
-        {properties, Properties},
-        {proto_ver, v5}
-    ]),
+    Defaults = #{
+        clean_start => true,
+        clientid => ClientId,
+        properties => Properties,
+        proto_ver => v5
+    },
+    Props = emqx_utils_maps:deep_merge(Defaults, StartProps),
+    {ok, Client} = emqtt:start_link(Props),
     {ok, _} = emqtt:connect(Client),
     on_exit(fun() -> catch emqtt:stop(Client) end),
     Client.
@@ -496,11 +499,21 @@ assert_monitor_metrics() ->
     ),
     ok.
 
+-define(assertReceiveReturn(PATTERN, TIMEOUT),
+    (fun() ->
+        receive
+            PATTERN = ____Msg0 -> ____Msg0
+        after TIMEOUT ->
+            error({message_not_received, ?LINE})
+        end
+    end)()
+).
+
 %%------------------------------------------------------------------------------
 %% Testcases
 %%------------------------------------------------------------------------------
 
-%% Smoke test where we have a single check and `all_pass' strategy.
+%% Smoke test where we have an example transfomration.
 t_smoke_test(_Config) ->
     Name1 = <<"foo">>,
     Operations = [
@@ -588,6 +601,65 @@ t_smoke_test(_Config) ->
 
     ok.
 
+%% A smoke test for a subset of read-only context fields.
+%%   * clientid
+%%   * id
+%%   * node
+%%   * peername
+%%   * publish_received_at
+%%   * username
+t_smoke_test_2(_Config) ->
+    Name1 = <<"foo">>,
+    Operations = [
+        operation(<<"payload.clientid">>, <<"clientid">>),
+        operation(<<"payload.id">>, <<"id">>),
+        operation(<<"payload.node">>, <<"node">>),
+        operation(<<"payload.peername">>, <<"peername">>),
+        operation(<<"payload.publish_received_at">>, <<"publish_received_at">>),
+        operation(<<"payload.username">>, <<"username">>),
+        operation(<<"payload.flags">>, <<"flags">>)
+    ],
+    Transformation1 = transformation(Name1, Operations),
+    {201, _} = insert(Transformation1),
+    ClientId = atom_to_binary(?FUNCTION_NAME),
+    C1 = connect(ClientId),
+    {ok, _, [_]} = emqtt:subscribe(C1, <<"t/#">>, [{qos, 2}]),
+    ok = publish(C1, <<"t/1">>, #{}),
+    {publish, #{payload := Payload0}} = ?assertReceiveReturn({publish, _}, 1_000),
+    NodeBin = atom_to_binary(node()),
+    ?assertMatch(
+        #{
+            <<"clientid">> := ClientId,
+            <<"id">> := <<_/binary>>,
+            <<"node">> := NodeBin,
+            <<"peername">> := <<"127.0.0.1:", _/binary>>,
+            <<"publish_received_at">> := PRAt,
+            <<"username">> := <<"undefined">>,
+            <<"flags">> := #{<<"dup">> := false, <<"retain">> := false}
+        } when is_integer(PRAt),
+        emqx_utils_json:decode(Payload0, [return_maps])
+    ),
+    %% Reconnect with an username.
+    emqtt:stop(C1),
+    Username = <<"myusername">>,
+    C2 = connect(ClientId, _IsPersistent = false, #{start_props => #{username => Username}}),
+    {ok, _, [_]} = emqtt:subscribe(C2, <<"t/#">>, [{qos, 2}]),
+    ok = publish(C2, <<"t/1">>, #{}),
+    {publish, #{payload := Payload1}} = ?assertReceiveReturn({publish, _}, 1_000),
+    ?assertMatch(
+        #{
+            <<"clientid">> := ClientId,
+            <<"id">> := <<_/binary>>,
+            <<"node">> := NodeBin,
+            <<"peername">> := <<"127.0.0.1:", _/binary>>,
+            <<"publish_received_at">> := PRAt,
+            <<"username">> := Username,
+            <<"flags">> := #{<<"dup">> := false, <<"retain">> := false}
+        } when is_integer(PRAt),
+        emqx_utils_json:decode(Payload1, [return_maps])
+    ),
+    ok.
+
 t_crud(_Config) ->
     ?assertMatch({200, []}, list()),