docs: function createByTwitter(profile, callback) {
    if (!profile.id) {
      return callback(new Error('Profile id is undefined'));
    }
  
    this.findByTwitterID(profile.id, ok(callback, (user) => {
      if (user) {
        return callback(null, user);
      }
  
      this.create({
        username: profile.username || null,
        name: profile.displayName,
      }, ok(callback, (newUser) => {
        newUser.addProvider('twitter', profile.id, profile, ok(callback, () => {
          callback(null, newUser);
        }));
      }));
    }));
  }