Generates the HMAC signature as required by the Adyen API.

generateAdyenSignature.js

import crypto from 'crypto';

// Docs: https://docs.adyen.com/developers/payments/accepting-payments/hmac-signature-calculation
export default function generateSignature(body, hmacKey) {
	const keys = Object
		.keys(body)
		// Step 1: Sort by keys
		.sort();
	
	const values = keys
		.map(key => body[key])
		// Step 2a: Replace falsy values with empty strings
		.map(value => ((value === null || value === undefined) ? '' : value.toString()))
		// Step 2b: Escape slashes and colons
		.map(value => value.replace(/\\/g, '\\\\').replace(/:/g, '\\:'));
	
	// Step 3: Concatenate the key names, first, followed by the values. Use a colon (“:”) to
	// delimit the key names and values
	const hashingInput = [...keys, ...values].join(':');
	
	// Step 4: Convert the HMAC key to the binary representation.
	const hmac = crypto.createHmac('sha256', new Buffer(hmacKey, 'hex'));
	hmac.update(hashingInput);

	// Step 5: Calculate the HMAC with the signing string
	// Step 6: Encode the result using the Base64 encoding scheme to obtain the signature.
	return hmac.digest('base64');
}

// Usage:
const testKey = '44782DEF547AAA06C910C43932B1EB0C71FC68D9D0C057550C48EC2ACF6BA056';
const body = {
	shopperLocale      : 'en_GB',
	merchantReference: 'paymentTest:143522\\64\\39255',
	merchantAccount  : 'TestMerchant',
	sessionValidity  : '2018-07-25T10:31:06Z',
	shipBeforeDate   : '2018-07-30',
	paymentAmount    : 1995,
	currencyCode     : 'EUR',
	skinCode         : 'X7hsNDWp',
};

generateSignature(body, testKey); // 8SFtIc6zQlswxAZqDKXL+BpRmlDvIWyjOwU8wdl0zK4=

My version of the same. Thanks for the Buffer hint on the hmacKey (slightly changed btw).

  // Verify incoming webhook.
  function verifyWebhook(payload) {

    const hmac = payload.additionalData.hmacSignature;
    const hmacKey = process.env.HMAC_KEY;

    const pspReference = payload.pspReference || '' ;
    const originalReference = payload.originalReference || '' ;
    const merchantAccountCode = payload.merchantAccountCode || '' ;
    const merchantReference = payload.merchantReference || '' ;
    const value = payload.amount.value.toString() || '' ;
    const currency = payload.amount.currency || '' ;
    const eventCode = payload.eventCode || '' ;
    const success = payload.success || '' ;

    let payloadToSign = pspReference + ':' + originalReference + ':' + merchantAccountCode + ':' + merchantReference + ':' + value + ':' + currency + ':' + eventCode + ':' + success;

    const genHash = crypto.createHmac("sha256", Buffer.from(hmacKey, 'hex'))
      .update(payloadToSign.toString(), "utf-8")
      .digest("base64");
    return genHash === hmac;
  }