config+sample-lnd.conf+lncfg: add RPC middleware config

sample-lnd.conf

@@ -1151,6 +1151,20 @@ litecoin.node=ltcd
 ; Defaults to the hostname.
 ; cluster.id=example.com
 
+[rpcmiddleware]
+
+; Enable the RPC middleware interceptor functionality.
+; rpcmiddleware.enable=true
+
+; Time after which a RPC middleware intercept request will time out and return
+; an error if it hasn't yet received a response.
+; rpcmiddleware.intercepttimeout=2s
+
+; Add the named middleware to the list of mandatory middlewares. All RPC
+; requests are blocked/denied if any of the mandatory middlewares is not
+; registered. Can be specified multiple times.
+; rpcmiddleware.addmandatory=my-example-middleware
+; rpcmiddleware.addmandatory=other-mandatory-middleware
 
 [bolt]