Optionally block enabling certain feature flags via Management UI/API

Useful to avoid accidentally enabling for example experiemental
feature flags from the Management UI on sensitive clusters.

deps/rabbitmq_management/priv/schema/rabbitmq_management.schema

@@ -646,3 +646,10 @@ end}.
     {datatype, {enum, [true, false]}},
     {include_default, false}
 ]}.
+
+%% Block enabling certain feature flags over API
+
+{mapping, "management.restrictions.feature_flag_blocked.$name", "rabbitmq_management.restrictions.feature_flag_blocked", [
+    {datatype, [string, {enum, [false]}]},
+    {include_default, false}
+]}.

deps/rabbitmq_management/src/rabbit_mgmt_features.erl

@@ -9,6 +9,7 @@
 
 -export([is_op_policy_updating_disabled/0,
          is_qq_replica_operations_disabled/0,
+         is_feature_flag_blocked/1,
          are_stats_enabled/0]).
 
 is_qq_replica_operations_disabled() ->
@@ -20,6 +21,13 @@ is_op_policy_updating_disabled() ->
         _ -> false
     end.
 
+-spec is_feature_flag_blocked(rabbit_feature_flags:feature_name()) -> {true, string()} | false.
+is_feature_flag_blocked(FeatureFlag) ->
+    case get_restriction([feature_flag_blocked, FeatureFlag]) of
+        Msg when is_list(Msg) -> {true, Msg};
+        _ -> false
+    end.
+
 are_stats_enabled() ->
     DisabledFromConf = application:get_env(
       rabbitmq_management, disable_management_stats, false),

deps/rabbitmq_management/src/rabbit_mgmt_wm_feature_flag_enable.erl

@@ -13,7 +13,6 @@
 -export([variances/2]).
 
 -include_lib("rabbitmq_management_agent/include/rabbit_mgmt_records.hrl").
--include_lib("rabbit_common/include/rabbit.hrl").
 
 %%--------------------------------------------------------------------
 
@@ -38,13 +37,18 @@ accept_content(ReqData, #context{} = Context) ->
     NameS = rabbit_mgmt_util:id(name, ReqData),
     try
         Name = list_to_existing_atom(binary_to_list(NameS)),
-        case rabbit_feature_flags:enable(Name) of
-            ok ->
-                {true, ReqData, Context};
-            {error, Reason1} ->
-                FormattedReason1 = rabbit_ff_extra:format_error(Reason1),
-                rabbit_mgmt_util:bad_request(
-                  list_to_binary(FormattedReason1), ReqData, Context)
+        case rabbit_mgmt_features:is_feature_flag_blocked(Name) of
+            {true, Message} ->
+                rabbit_mgmt_util:method_not_allowed(Message, ReqData, Context);
+            false ->
+                case rabbit_feature_flags:enable(Name) of
+                    ok ->
+                        {true, ReqData, Context};
+                    {error, Reason1} ->
+                        FormattedReason1 = rabbit_ff_extra:format_error(Reason1),
+                        rabbit_mgmt_util:bad_request(
+                          list_to_binary(FormattedReason1), ReqData, Context)
+                end
         end
     catch
         _:badarg ->

deps/rabbitmq_management/test/rabbit_mgmt_http_SUITE.erl

@@ -159,6 +159,7 @@ all_tests() -> [
     user_limit_set_test,
     config_environment_test,
     disabled_qq_replica_opers_test,
+    feature_flag_blocked_test,
     list_deprecated_features_test,
     list_used_deprecated_features_test
 ].
@@ -230,6 +231,11 @@ init_per_testcase(Testcase = disabled_qq_replica_opers_test, Config) ->
     rabbit_ct_broker_helpers:rpc_all(Config,
       application, set_env, [rabbitmq_management, restrictions, Restrictions]),
     rabbit_ct_helpers:testcase_started(Config, Testcase);
+init_per_testcase(Testcase = feature_flag_blocked_test, Config) ->
+    Restrictions = [{feature_flag_blocked, [{khepri_db, "Khepri is blocked"}]}],
+    rabbit_ct_broker_helpers:rpc_all(Config,
+      application, set_env, [rabbitmq_management, restrictions, Restrictions]),
+    rabbit_ct_helpers:testcase_started(Config, Testcase);
 init_per_testcase(queues_detailed_test, Config) ->
     IsEnabled = rabbit_ct_broker_helpers:is_feature_flag_enabled(
                   Config, detailed_queues_endpoint),
@@ -302,6 +308,10 @@ end_per_testcase0(disabled_qq_replica_opers_test, Config) ->
     rabbit_ct_broker_helpers:rpc(Config, 0, application, unset_env,
                                  [rabbitmq_management, restrictions]),
     Config;
+end_per_testcase0(feature_flag_blocked_test, Config) ->
+    rabbit_ct_broker_helpers:rpc(Config, 0, application, unset_env,
+                                 [rabbitmq_management, restrictions]),
+    Config;
 end_per_testcase0(Testcase, Config)
   when Testcase == list_deprecated_features_test;
        Testcase == list_used_deprecated_features_test ->
@@ -3716,6 +3726,11 @@ disabled_qq_replica_opers_test(Config) ->
     http_delete(Config, "/queues/quorum/replicas/on/" ++ Nodename ++ "/shrink", ?METHOD_NOT_ALLOWED),
     passed.
 
+feature_flag_blocked_test(Config) ->
+    Body = "",
+    http_put(Config, "/feature-flags/khepri_db/enable", Body, ?METHOD_NOT_ALLOWED),
+    passed.
+
 list_deprecated_features_test(Config) ->
     Desc = "This is a deprecated feature",
     DocUrl = "https://rabbitmq.com/",