Authentication plugin acl_check function is passed local_username for local bridges.

src/security.c

@@ -194,13 +194,23 @@ int mosquitto_security_cleanup(struct mosquitto_db *db, bool reload)
 
 int mosquitto_acl_check(struct mosquitto_db *db, struct mosquitto *context, const char *topic, int access)
 {
+	char *username;
+
 	if(!context->id){
 		return MOSQ_ERR_ACL_DENIED;
 	}
 	if(!db->auth_plugin.lib){
 		return mosquitto_acl_check_default(db, context, topic, access);
 	}else{
-		return db->auth_plugin.acl_check(db->auth_plugin.user_data, context->id, context->username, topic, access);
+#ifdef WITH_BRIDGE
+		if(context->bridge){
+			username = context->bridge->local_username;
+		}else
+#endif
+		{
+			username = context->username;
+		}
+		return db->auth_plugin.acl_check(db->auth_plugin.user_data, context->id, username, topic, access);
 	}
 }