code: function _linkIdentity(userId, key, socialUserInfo, creds) {
      var identityOptions = {
              id: socialUserInfo.id,
              accessToken: creds.access_token,
              screen_name: socialUserInfo.username
          };
  
      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.