diff --git a/apps/emqx/rebar.config b/apps/emqx/rebar.config
index 31caa498d..3d016a461 100644
--- a/apps/emqx/rebar.config
+++ b/apps/emqx/rebar.config
@@ -17,7 +17,7 @@
     , {esockd, {git, "https://github.com/emqx/esockd", {tag, "5.9.0"}}}
     , {ekka, {git, "https://github.com/emqx/ekka", {tag, "0.11.1"}}}
     , {gen_rpc, {git, "https://github.com/emqx/gen_rpc", {tag, "2.5.1"}}}
-    , {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.22.1"}}}
+    , {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.22.3"}}}
     , {pbkdf2, {git, "https://github.com/emqx/erlang-pbkdf2.git", {tag, "2.0.4"}}}
     , {recon, {git, "https://github.com/ferd/recon", {tag, "2.5.1"}}}
     , {snabbkaffe, {git, "https://github.com/kafka4beam/snabbkaffe.git", {tag, "0.16.0"}}}
diff --git a/apps/emqx_authz/src/emqx_authz_http.erl b/apps/emqx_authz/src/emqx_authz_http.erl
index 3721aef28..5ee0a6d94 100644
--- a/apps/emqx_authz/src/emqx_authz_http.erl
+++ b/apps/emqx_authz/src/emqx_authz_http.erl
@@ -124,14 +124,14 @@ generate_request( PubSub
     case Method of
         get  ->
             NPath = append_query(Path, NBaseQuery ++ Body),
-            {NPath, maps:to_list(Headers)};
+            {NPath, Headers};
         _ ->
             NPath = append_query(Path, NBaseQuery),
             NBody = serialize_body(
                       maps:get(<<"Accept">>, Headers, <<"application/json">>),
                       Body
                      ),
-            {NPath, maps:to_list(Headers), NBody}
+            {NPath, Headers, NBody}
     end.
 
 append_query(Path, []) ->
diff --git a/apps/emqx_authz/src/emqx_authz_schema.erl b/apps/emqx_authz/src/emqx_authz_schema.erl
index 752d656ba..d68d97cf3 100644
--- a/apps/emqx_authz/src/emqx_authz_schema.erl
+++ b/apps/emqx_authz/src/emqx_authz_schema.erl
@@ -33,6 +33,7 @@
         ]).
 
 -import(emqx_schema, [mk_duration/2]).
+-include_lib("hocon/include/hoconsc.hrl").
 
 %%--------------------------------------------------------------------
 %% Hocon Schema
@@ -158,20 +159,20 @@ validations() ->
     , {check_headers, fun check_headers/1}
     ].
 
-headers(type) -> map();
+headers(type) -> list({binary(), binary()});
 headers(converter) ->
     fun(Headers) ->
-       maps:merge(default_headers(), transform_header_name(Headers))
+        maps:to_list(maps:merge(default_headers(), transform_header_name(Headers)))
     end;
-headers(default) -> default_headers();
+headers(default) -> maps:to_list(default_headers());
 headers(_) -> undefined.
 
-headers_no_content_type(type) -> map();
+headers_no_content_type(type) -> list({binary(), binary()});
 headers_no_content_type(converter) ->
     fun(Headers) ->
-       maps:merge(default_headers_no_content_type(), transform_header_name(Headers))
+       maps:to_list(maps:merge(default_headers_no_content_type(), transform_header_name(Headers)))
     end;
-headers_no_content_type(default) -> default_headers_no_content_type();
+headers_no_content_type(default) -> maps:to_list(default_headers_no_content_type());
 headers_no_content_type(_) -> undefined.
 
 url(type) -> binary();
@@ -221,7 +222,7 @@ check_headers(Conf)
 check_headers(Conf) ->
     Method = to_bin(hocon_schema:get_value("config.method", Conf)),
     Headers = hocon_schema:get_value("config.headers", Conf),
-    Method =:= <<"post">> orelse (not maps:is_key(<<"content-type">>, Headers)).
+    Method =:= <<"post">> orelse (not lists:member(<<"content-type">>, Headers)).
 
 union_array(Item) when is_list(Item) ->
     hoconsc:array(hoconsc:union(Item)).
diff --git a/apps/emqx_connector/src/emqx_connector_http.erl b/apps/emqx_connector/src/emqx_connector_http.erl
index 8b366070d..42bfe85b1 100644
--- a/apps/emqx_connector/src/emqx_connector_http.erl
+++ b/apps/emqx_connector/src/emqx_connector_http.erl
@@ -262,11 +262,20 @@ preprocess_request(#{
      , request_timeout => maps:get(request_timeout, Req, 30000)
      }.
 
-preproc_headers(Headers) ->
+preproc_headers(Headers) when is_map(Headers) ->
     maps:fold(fun(K, V, Acc) ->
-            Acc#{emqx_plugin_libs_rule:preproc_tmpl(bin(K)) =>
-                 emqx_plugin_libs_rule:preproc_tmpl(bin(V))}
-        end, #{}, Headers).
+            [{
+                emqx_plugin_libs_rule:preproc_tmpl(bin(K)),
+                emqx_plugin_libs_rule:preproc_tmpl(bin(V))
+            } | Acc]
+        end, [], Headers);
+preproc_headers(Headers) when is_list(Headers) ->
+    lists:map(fun({K, V}) ->
+        {
+            emqx_plugin_libs_rule:preproc_tmpl(bin(K)),
+            emqx_plugin_libs_rule:preproc_tmpl(bin(V))
+        }
+              end, Headers).
 
 process_request(#{
             method := MethodTks,
@@ -278,7 +287,7 @@ process_request(#{
     Conf#{ method => make_method(emqx_plugin_libs_rule:proc_tmpl(MethodTks, Msg))
          , path => emqx_plugin_libs_rule:proc_tmpl(PathTks, Msg)
          , body => process_request_body(BodyTks, Msg)
-         , headers => maps:to_list(proc_headers(HeadersTks, Msg))
+         , headers => proc_headers(HeadersTks, Msg)
          , request_timeout => ReqTimeout
          }.
 
@@ -288,10 +297,12 @@ process_request_body(BodyTks, Msg) ->
     emqx_plugin_libs_rule:proc_tmpl(BodyTks, Msg).
 
 proc_headers(HeaderTks, Msg) ->
-    maps:fold(fun(K, V, Acc) ->
-            Acc#{emqx_plugin_libs_rule:proc_tmpl(K, Msg) =>
-                 emqx_plugin_libs_rule:proc_tmpl(V, Msg)}
-        end, #{}, HeaderTks).
+    lists:map(fun({K, V}) ->
+            {
+                emqx_plugin_libs_rule:proc_tmpl(K, Msg),
+                emqx_plugin_libs_rule:proc_tmpl(V, Msg)
+            }
+              end, HeaderTks).
 
 make_method(M) when M == <<"POST">>; M == <<"post">> -> post;
 make_method(M) when M == <<"PUT">>; M == <<"put">> -> put;
diff --git a/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl b/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl
index be8b4d074..1fbdb9eca 100644
--- a/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl
+++ b/apps/emqx_dashboard/src/emqx_dashboard_swagger.erl
@@ -436,6 +436,7 @@ typename_to_spec("timeout()", _Mod) -> #{<<"oneOf">> => [#{type => string, examp
 typename_to_spec("bytesize()", _Mod) -> #{type => string, example => <<"32MB">>};
 typename_to_spec("wordsize()", _Mod) -> #{type => string, example => <<"1024KB">>};
 typename_to_spec("map()", _Mod) -> #{type => object, example => #{}};
+typename_to_spec("{binary(), binary()}", _Mod) -> #{type => object, example => #{}};
 typename_to_spec("comma_separated_list()", _Mod) ->
     #{type => string, example => <<"item1,item2">>};
 typename_to_spec("comma_separated_atoms()", _Mod) ->
diff --git a/rebar.config b/rebar.config
index 61a3f4510..91a2aca1c 100644
--- a/rebar.config
+++ b/rebar.config
@@ -65,7 +65,7 @@
     , {system_monitor, {git, "https://github.com/klarna-incubator/system_monitor", {tag, "2.2.0"}}}
     , {getopt, "1.0.2"}
     , {snabbkaffe, {git, "https://github.com/kafka4beam/snabbkaffe.git", {tag, "0.16.0"}}}
-    , {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.22.1"}}}
+    , {hocon, {git, "https://github.com/emqx/hocon.git", {tag, "0.22.3"}}}
     , {emqx_http_lib, {git, "https://github.com/emqx/emqx_http_lib.git", {tag, "0.4.1"}}}
     , {esasl, {git, "https://github.com/emqx/esasl", {tag, "0.2.0"}}}
     , {jose, {git, "https://github.com/potatosalad/erlang-jose", {tag, "1.11.2"}}}