docs: refine authn and auth config docs

apps/emqx/src/emqx_access_control.erl

@@ -63,4 +63,5 @@ do_authorize(ClientInfo, PubSub, Topic) ->
 
 -compile({inline, [run_hooks/3]}).
 run_hooks(Name, Args, Acc) ->
-    ok = emqx_metrics:inc(Name), emqx_hooks:run_fold(Name, Args, Acc).
+    ok = emqx_metrics:inc(Name),
+    emqx_hooks:run_fold(Name, Args, Acc).

apps/emqx/src/emqx_schema.erl

@@ -108,9 +108,27 @@ in <code>zone</code> configs"""
           })}
     , {?EMQX_AUTHENTICATION_CONFIG_ROOT_NAME,
        authentication(
-"""Default authentication configs for all MQTT listeners.<br>
+"""Default authentication configs for all MQTT listeners.
+<br>
 For per-listener overrides see <code>authentication</code>
-in listener configs""")}
+in listener configs
+<br>
+<br>
+EMQ X can be configured with:
+<br>
+<ul>
+<li><code>[]</code>: The default value, it allows *ALL* logins</li>
+<li>one: For example <code>{enable:true,backend:\"built-in-database\",mechanism=\"password-based\"}</code></li>
+<li>chain: An array of structs.</li>
+</ul>
+<br>
+When a chain is configured, the login credentials are checked against the backends
+per the configured order, until an 'allow' or 'deny' decision can be made.
+<br>
+If there is no decision after a full chain exhaustion, the login is rejected.
+""")}
+    %% NOTE: authorization schema here is only to keep emqx app prue
+    %% the full schema for EMQ X node is injected in emqx_conf_schema.
     , {"authorization",
        sc(ref("authorization"),
           #{})}

apps/emqx_conf/src/emqx_conf_schema.erl

@@ -68,8 +68,7 @@ roots() ->
         undefined -> persistent_term:put(PtKey, emqx_authn_schema);
         _ -> ok
     end,
-    %% authorization configs are merged in THIS schema's "authorization" fields
-    lists:keydelete("authorization", 1, emqx_schema:roots(high)) ++
+    emqx_schema_high_prio_roots() ++
     [ {"node",
        sc(hoconsc:ref("node"),
           #{ desc => "Node name, cookie, config & data directories "
@@ -93,20 +92,6 @@ roots() ->
                      "should work, but in case you need to do performance "
                      "fine-turning or experiment a bit, this is where to look."
            })}
-    , {"authorization",
-       sc(hoconsc:ref("authorization"),
-          #{ desc => """
-Authorization a.k.a ACL.<br>
-In EMQ X, MQTT client access control is extremly flexible.<br>
-An out of the box set of authorization data sources are supported.
-For example,<br>
-'file' source is to support concise and yet generic ACL rules in a file;<br>
-'built-in-database' source can be used to store per-client customisable rule sets,
-natively in the EMQ X node;<br>
-'http' source to make EMQ X call an external HTTP API to make the decision;<br>
-'postgresql' etc. to look up clients or rules from external databases;<br>
-"""
-           })}
     , {"db",
        sc(ref("db"),
           #{ desc => "Settings of the embedded database."
@@ -849,3 +834,22 @@ ensure_list(V) ->
 
 roots(Module) ->
     lists:map(fun({_BinName, Root}) -> Root end, hocon_schema:roots(Module)).
+
+%% Like authentication schema, authorization schema is incomplete in emqx_schema
+%% module, this function replaces the root filed "authorization" with a new schema
+emqx_schema_high_prio_roots() ->
+    Roots = emqx_schema:roots(high),
+    Authz = {"authorization",
+             sc(hoconsc:ref("authorization"),
+             #{ desc => """
+Authorization a.k.a ACL.<br>
+In EMQ X, MQTT client access control is extremly flexible.<br>
+An out of the box set of authorization data sources are supported.
+For example,<br>
+'file' source is to support concise and yet generic ACL rules in a file;<br>
+'built-in-database' source can be used to store per-client customisable rule sets,
+natively in the EMQ X node;<br>
+'http' source to make EMQ X call an external HTTP API to make the decision;<br>
+'postgresql' etc. to look up clients or rules from external databases;<br>
+""" })},
+    lists:keyreplace("authorization", 1, Roots, Authz).