Supabase Send Email hook - Signature check with Express Typescript app

app.ts

import cors from 'cors';
import express from 'express';
import helmet from 'helmet';
import morgan from 'morgan';

const app = express();

app.use(morgan('dev'));
app.use(helmet());
app.use(cors());

app.use(
  '/api/v1/auth/email',
  // Ensure that req.body is a raw text.
  express.text({ type: ['*/text', 'application/json'] }), 
  // Keep this router above the json middleware to be able to provide the raw body to
  // the Signature checking method.
  authEmailRouter,
);

// Other routers below.

export default app;

email.ts

import { Webhook } from 'standardwebhooks';
import express, { Request } from 'express';
import { env } from '../../env';

const router = express.Router({ mergeParams: true });

const checkSignature = async (req: Request) => {
  const bodyAsText = await req.body;

  const webhook = new Webhook(
    env.SUPABASE_EMAIL_WEBHOOK_SECRET.replace('v1,whsec_', ''),
  );

  try {
    const parsedData = webhook.verify(
      bodyAsText,
      // @ts-expect-error - Not important.
      req.headers,
    );
    return parsedData;
  } catch {
    return null;
  }
};

router.post('/webhook', async (req, res) => {
  const payload = await checkSignature(req);
  if (!payload) {
    return res
      .status(403)
      .setHeader('Content-Type', 'application/json')
      .json({ error: 'Unauthorized' })
      .end();
  }
  // TODO: Send email.
  return res
    .status(200)
    .setHeader('Content-Type', 'application/json')
    .json({ message: 'OK' })
    .end();
});

export default router;