Auth0 Action for the Discord Guild Member Authorization

action.js

const { Client, Intents } = require('discord.js');

/**
* Handler that will be called during the execution of a PostLogin flow.
*
* @param {Event} event - Details about the user and the context in which they are logging in.
* @param {PostLoginAPI} api - Interface whose methods can be used to change the behavior of the login.
*/
exports.onExecutePostLogin = async (event, api) => {
  const identities = event.user.identities.filter((v) => { return v.connection == "discord"; });
  const identity = identities.length == 1 ? identities[0] : null;
  if (!identity) {
    api.access.deny("this user isn't authenticated with discord");
    return;
  }
  const result = identity.user_id?.match(/discord\|(.+)/);
  if (result?.length != 2) {
    api.access.deny("the format of user_id is invalid");
  }
  const userID = result?.length == 2 ? result[1] : null;

  const client = new Client({ intents: [Intents.FLAGS.GUILDS] });
  client.login(event.secrets.DISCORD_BOT_TOKEN);
  const isUserMember = await client.guilds.fetch(event.secrets.DISCORD_GUILD_ID)
    .then((guild) => {
      return guild.members.fetch(userID)
        .then(() => { return true; })
        .catch((e) => { console.warn(e); }); // TODO(musaprg): do better error handling
  });
  if (!isUserMember) {
    api.access.deny("You are not a member of the Miscord. Please contact the administrator for details.");
    return;
  }
};