Code to make Discord interactions endpoints created in n8n work. Set the environmental variable NODE_FUNCTION_ALLOW_EXTERNAL to contain tweetnacl, otherwise it won't work!

code.js

const nacl = require('tweetnacl');

const PUBLIC_KEY = 'APPLICATIONPUBLICKEY';

if (!items || items.length === 0) {
  return [
    {
      json: {
        error: 'Invalid payload'
      }
    }
  ];
}

const interaction = items[0].json;

if (!interaction.headers) {
  return [
    {
      json: {
        error: 'Missing headers'
      }
    }
  ];
}

const signature = interaction.headers['x-signature-ed25519'];
const timestamp = interaction.headers['x-signature-timestamp'];
const body = JSON.stringify(interaction.body);

if (!signature || !timestamp) {
  return [
    {
      json: {
        error: 'Missing signature or timestamp'
      }
    }
  ];
}

const isVerified = nacl.sign.detached.verify(
  Buffer.from(timestamp + body),
  Buffer.from(signature, 'hex'),
  Buffer.from(PUBLIC_KEY, 'hex')
);

if (!isVerified) {
  return [
    {
      json: {
        error: 'Invalid request signature'
      }
    }
  ];
}

return items;