Unable to correctly verify Slack requests

Here is a working example of how to verify a Slack request, it also supports slash commands:

Slack bot event example	Run in Fusebit

  import crypto from 'crypto';
  import formurlencoded from 'form-urlencoded';

  export const validateSlackRequest = (
    requestSignature: string,
    timestampHeader: string, // Get it from the request header x-slack-request-timestamp
    contentType: string, // Get it from the request header content-type
    signingSecret: string,
    timestamp: string,
    body: string,
  ) => {
      
    let rawBody;
    if (contentType?.toLocaleLowerCase() === 'application/x-www-form-urlencoded') {
      // Slash commands are sent in this content type
      rawBody = formurlencoded(body);
    } else {
      rawBody = JSON.stringify(body)
        .replace(/\//g, '\\/')
        .replace(/[\u007f-\uffff]/g, (c) => '\\u' + ('0000' + c.charCodeAt(0).toString(16)).slice(-4));
    }

    const basestring = ['v0', timestampHeader, rawBody].join(':');
    const calculatedSignature = 'v0=' + crypto.createHmac('sha256', signingSecret).update(basestring).digest('hex');
    const calculatedSignatureBuffer = Buffer.from(calculatedSignature, 'utf8');
    const requestSignatureBuffer = Buffer.from(requestSignature, 'utf8');
    return crypto.timingSafeEqual(calculatedSignatureBuffer, requestSignatureBuffer);
  };