@pokutuna/express-validate-slack

A express middleware to verify requests from Slack.

Based on Verifying requests from Slack | Slack

Usage

import express from "express";
import verifySlack, { rawBodyKeeper } from "express-validate-slack";

const app = express();

// 1. To keep original request body as `req.rawBody`.
// Almost all middlewares & frameworks replace `req.body`.
// Verifying requests from Slack requires original body.
//
// This middleware first checks req.rawBody,
// and use req.body if rawBody doesn't exist.
app.use(express.json({ verify: rawBodyKeeper }));


// 2. Enable this middleware
app.use(verifySlack("<SLACK_SIGNING_SECRET>"));

// or enable middleware for a route.
// see https://expressjs.com/en/guide/using-middleware.html
app.post(
  "/slack/slash-command",
  verifySlack("<SLACK_SIGNING_SECRET>"),
  (req, res) => {
    ...
  }
);

Appendix

Cloud Functions

This package is designed for Google Cloud Functions.

You don't need to keep req.rawBody(Step 1 in Usage) when receiving reqeusts on Cloud Functions.

The rawBody property contains the unparsed bytes of the request body.
HTTP Functions | Cloud Functions Documentation | Google Cloud

Next.js

To use this with Next.js in API Routes, do the following.

API Routes: API Middlewares | Next.js

In pages/api/slack.ts

import type { NextApiRequest, NextApiResponse } from "next";
import type express from "express";
import bodyParser from "body-parser";
import validateSlack, { rawBodyKeeper } from "@pokutuna/express-validate-slack";

export const config = {
  api: {
    bodyParser: false,
  },
};

// runMiddleware from Next.js document
// https://nextjs.org/docs/api-routes/api-middlewares#connectexpress-middleware-support
function runMiddleware(req: NextApiRequest, res: NextApiResponse, fn: express.RequestHandler) {
  return new Promise((resolve, reject) => {
    fn(req, res, (result) => {
      if (result instanceof Error) {
        return reject(result);
      }
      return resolve(result);
    });
  });
}

export default async function handler(req: NextApiRequest, res: NextApiResponse) {
  // Run middlewares
  await runMiddleware(req, res, bodyParser.json({ verify: rawBodyKeeper }));
  await runMiddleware(req, res, validateSlack("<SLACK_SIGNING_SECRET>"));

  // Rest of API logic

  // e.g. URL Verification https://api.slack.com/events/url_verification
  if (req.body.type === "url_verification") {
    const { challenge } = req.body;
    return res.status(200).json({ challenge });
  }

  res.status(200).json({/* ... */});
}