add username_regex

config-example.json

@@ -121,5 +121,6 @@
     "type": "like-google-fonts",
     "url": "https://fonts.loli.net"
   },
-  "no_cdn": false
+  "no_cdn": false,
+  "username_regex": "^[a-zA-Z0-9\\-\\_]+$"
 }

utility.js

@@ -255,7 +255,7 @@ module.exports = {
     return md5.digest('hex');
   },
   isValidUsername(s) {
-    return /^[a-zA-Z0-9\-\_]+$/.test(s);
+    return RegExp(syzoj.config.username_regex).test(s);
   },
   locks: [],
   lock(key, cb) {