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Slack Request Verification

Slack has deprecated the previous method of comparing the verification token to the request's verification token. The below snippet implements the new signing secret method in JavaScript.

import { createHmac } from 'crypto'

// pull out the slack request timestamp and signature to compare against
const timestamp = headers['X-Slack-Request-Timestamp']
const actual = headers['X-Slack-Signature']

// use the **raw** body of the request here before middleware parses it (if necessary)
const rawBody = ctx.request.body.raw

// combine the requred fields
const baseString = ['v0', timestamp, rawBody].join(':')

// hash them together
const hash = createHmac('sha256', "YOUR_SLACK_SIGNING_SECRET")

// prepend the version
const computed = `v0=${hash}`

// make the comparison
if (computed !== actual) {
  // failed to verify - exit here

// succesfully verified - continue