feat: add create hmac signature (#500)

**This PR adds new function to the utility package.**

Function `createHmacSignature()` will be used in Apify SDK as well as in
Apify Core repositories

Author: danpoletaev

packages/utilities/src/hmac.ts

@@ -0,0 +1,36 @@
+import crypto from 'crypto';
+
+const CHARSET = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');
+
+/**
+ * Encodes BigInt to base62.
+ */
+function encodeBase62(num: bigint) {
+    if (num === 0n) {
+        return CHARSET[0];
+    }
+
+    let res = '';
+    while (num > 0n) {
+        res = CHARSET[Number(num % 62n)] + res;
+        num /= 62n;
+    }
+    return res;
+}
+
+/**
+ * Generates an HMAC signature and encodes it using Base62.
+ * Base62 encoding reduces the signature length.
+ *
+ * @param secretKey {string} Secret key used for signing signatures
+ * @param message {string} Message to be signed
+ * @returns string
+ */
+export function createHmacSignature(secretKey: string, message: string): string {
+    const signature = crypto.createHmac('sha256', secretKey)
+        .update(message)
+        .digest('hex')
+        .substring(0, 30);
+
+    return encodeBase62(BigInt(`0x${signature}`));
+}

packages/utilities/src/index.ts

@@ -8,3 +8,4 @@ export * from './webhook_payload_template';
 export * from './crypto';
 export * from './url_params_utils';
 export * from './code_hash_manager';
+export * from './hmac';

test/hmac.test.ts

@@ -0,0 +1,17 @@
+import { createHmacSignature } from '@apify/utilities';
+
+describe('createHmacSignature()', () => {
+    it('should create a valid HMAC signature', () => {
+        const secretKey = 'hmac-secret-key';
+        const message = 'hmac-message-to-be-authenticated';
+        expect(createHmacSignature(secretKey, message)).toBe('pcVagAsudj8dFqdlg7mG');
+    });
+
+    it('should create same HMAC signature, when secretKey and message are same', () => {
+        const secretKey = 'hmac-same-secret-key';
+        const message = 'hmac-same-message-to-be-authenticated';
+        for (let i = 0; i < 5; i++) {
+            expect(createHmacSignature(secretKey, message)).toBe('FYMcmTIm3idXqleF1Sw5');
+        }
+    });
+});