Firebase Functions listener for EAS webhook

Expo Application Services (EAS)
1

I’m trying to write a Firebase Cloud function to receive EAS webhook notifications. I used the Express sample code from here: Webhooks - Expo Documentation as a starting point, but can’t get the signatures to match.

  export const easWebhookListener = functions.https
  .onRequest(async (req, res) => {
    const expoSignature = req.headers['expo-signature'];
    const hmac = crypto.createHmac('sha1', functions.config().easwebhook.key);
    hmac.update(req.rawBody.toString());
    const hash = `sha1=${hmac.digest('hex')}`;
    if (
      expoSignature?.length !== hash.length ||
      !crypto.timingSafeEqual(
        Buffer.from(expoSignature as string, 'utf8'),
        Buffer.from(hash, 'utf8')
      )
    ) {
      console.error('Signatures do not match!');
      res.status(500).send("Signatures didn't match!");
    } else {
      // never gets here
      res.send('OK!');
    }
  });

I have checked that functions.config().easwebhook.key returns the correct value. I suppose req.rawBody.toString() might be the wrong way to parse the request data.

Any ideas about what I’m doing wrong or what I could try?

2

Try to import/use body-parser, then use it as a middleware so requests body is parsed for you magically, and then you can access the payload via req.body :wink: