code: function _linkIdentity(userId, key, socialUserInfo, creds) {
      var identityOptions = {
              id: socialUserInfo.id_str,
              screen_name: socialUserInfo.screen_name,
              accessToken: creds.oauth_token,
              accessSecret: creds.oauth_token_secret
          };
  
      return db.users.linkIdentity(userId, key, identityOptions);
  }
docs: When a user is already in the system and the email matches, then we would update their social data with the newly supplied info.