Programming in Node.js and using Zoom Web SDK? Here is an example utility module to generate the signature as required, and documented here (in PHP): https://zoom.github.io/zoom-sdk-web/global.html#generate_signature

zoom-web-sdk-node-generate-signature-module.js

'use strict';

// Determine if crypto support is available
let crypto;
try {
    crypto = require('crypto');
} catch (err) {
    console.error('crypto support is unavailable');
    throw err;
}

// NOTE: Best practice is to load the Zoom API Keys from environment files, not hardcoded
const APP_KEY       = process.env.ZOOM_APP_KEY;
const APP_SECRET    = process.env.ZOOM_APP_SECRET;

// Define this module
let ZoomUtil = {};

ZoomUtil.rtrim = (targetString, characterList) {
  // NOTE: This method was borrowed from here (I have not tested it)...
  //  discuss at: http://locutus.io/php/rtrim/
  // original by: Kevin van Zonneveld (http://kvz.io)
  //    input by: Erkekjetter
  //    input by: rem
  // improved by: Kevin van Zonneveld (http://kvz.io)
  // bugfixed by: Onno Marsman (https://twitter.com/onnomarsman)
  // bugfixed by: Brett Zamir (http://brett-zamir.me)
  //   example 1: rtrim('    Kevin van Zonneveld    ')
  //   returns 1: '    Kevin van Zonneveld'

  charlist = !charlist ? ' \\s\u00A0' : (charlist + '')
    .replace(/([[\]().?/*{}+$^:])/g, '\\$1')

  var re = new RegExp('[' + charlist + ']+$', 'g')

  return (str + '').replace(re, '')
}
};

ZoomUtil.generateHash = function (string) {
    // USING HMAC
    let hmac = crypto.createHmac('sha256', new Buffer(APP_SECRET, 'utf8'));
    hmac.update(string);
    let signature = hmac.digest('hex');

    // Base64 encoded the hash
    let tmpSig = new Buffer(signature).toString('base64');

    // NOTE: Untested code below, just following what the  PHP example code (may not be necessary)
    // replacing all instances of `+/`  within tmpSig to `-_` and then trimming all whitespace and 
    // hyphens from the end of the string
    let regex = /\+\//;
    return this.rtrim(tmpSig.replace(regex, `-_`), '='); // According to the PHP example, this should now be a URL safe base64 encoded signature.
};

ZoomUtil.generateSignatureString = function (meetingNumber = 0, role = 1) {
    /**
    NOTE: there are constants which are expected to be loaded from an environment file (a best practice for any Zoom API Keys)
    // Uncomment to debug if needed
    console.log('Inside buildRequestHash()');
    console.log('meetingNumber: ', meetingNumber);
    console.log('role: ', role);
    **/

    let errorMsgs = [];

    // Ensure data is provided as needed by Zoom Web SDK and related Zoom API.
    // NOTE: This logic check could be greatly improved, but it should work for demonstration purposes
    if(0 === meetingNumber) {
        errorMsgs.push('Invalid argument, `meetingNumber` is required. More info: https://zoom.github.io/zoom-sdk-web/global.html#generate_signature');
    }

    let time = +new Date(); // Unix timestamp (milliseconds since epoch

    // NOTE: Possible values for `role`: 0 is for participant, 1 is for host
    // Construct the content string required by generateHash()
    let content = new Buffer(`${appKey}${meetingNumber}${time}${role}`).toString('base64');

    if(0 !== errorMsgs.length) {
        console.error(errorMsgs);
    }

    //console.log('RAW CONTENT: ', content);
    return this.generateHash(content);
};

module.exports = ZoomUtil;