text: module.exports = req => {
      let {user_info} = req.session;
      return new Promise((resolve, reject) => {
          if(!user_info) reject("Not authorized.");
          else {
              let {user, classroom} = user_info;
              if(!user || !classroom || !user.id || !user.email || !user.name) reject("Not authorized.");
              else resolve(user_info);
          }
      });
  }