feat(signup): allow . and _ in usernames

config/modules/validations.js

@@ -29,4 +29,7 @@ module.exports = {
   team: {
     global: Joi.boolean().allow(null),
   },
+  user: {
+    username: Joi.string().regex(/^[a-zA-Z0-9_.]+$/),
+  },
 }