Warn if neither --rpc-secret nor a combination of --rpc-user/rpc-passwd is set

src/DownloadEngineFactory.cc

@@ -196,6 +196,12 @@ DownloadEngineFactory::newDownloadEngine
                                                           e.get(), pid));
   }
   if(op->getAsBool(PREF_ENABLE_RPC)) {
+    if(op->get(PREF_RPC_SECRET).empty() && op->get(PREF_RPC_USER).empty()) {
+      A2_LOG_WARN("Neither --rpc-secret nor a combination of --rpc-user and "
+                  "--rpc-passwd is set. This is insecure. It is extremely "
+                  "recommended to specify --rpc-secret with the adequate "
+                  "secrecy or now deprecated --rpc-user and --rpc-passwd.");
+    }
     bool ok = false;
     bool secure = op->getAsBool(PREF_RPC_SECURE);
     if(secure) {