fix(node/crypto): support promisify on generateKeyPair (#26913)

Calling `promisify(generateKeyPair)` didn't work as expected. It
requires a custom promisify implementation.

This was easy to fix thanks to the excellent debugging investigation in
https://github.com/denoland/deno/issues/26910

Fixes https://github.com/denoland/deno/issues/26910

Co-authored-by: Bartek Iwańczuk <biwanczuk@gmail.com>

ext/node/polyfills/internal/crypto/keygen.ts

@@ -30,6 +30,7 @@ import {
 import { Buffer } from "node:buffer";
 import { KeyFormat, KeyType } from "ext:deno_node/internal/crypto/types.ts";
 import process from "node:process";
+import { promisify } from "node:util";
 
 import {
   op_node_generate_dh_group_key,
@@ -570,7 +571,15 @@ export function generateKeyPair(
     privateKey: any,
   ) => void,
 ) {
-  createJob(kAsync, type, options).then((pair) => {
+  _generateKeyPair(type, options)
+    .then(
+      (res) => callback(null, res.publicKey, res.privateKey),
+      (err) => callback(err, null, null),
+    );
+}
+
+function _generateKeyPair(type: string, options: unknown) {
+  return createJob(kAsync, type, options).then((pair) => {
     const privateKeyHandle = op_node_get_private_key_from_pair(pair);
     const publicKeyHandle = op_node_get_public_key_from_pair(pair);
 
@@ -589,12 +598,15 @@ export function generateKeyPair(
       }
     }
 
-    callback(null, publicKey, privateKey);
+    return { publicKey, privateKey };
-  }).catch((err) => {
-    callback(err, null, null);
   });
 }
 
+Object.defineProperty(generateKeyPair, promisify.custom, {
+  enumerable: false,
+  value: _generateKeyPair,
+});
+
 export interface KeyPairKeyObjectResult {
   publicKey: KeyObject;
   privateKey: KeyObject;

tests/unit_node/crypto/crypto_key_test.ts

@@ -677,3 +677,26 @@ Deno.test("generateKeyPair large pem", function () {
     },
   });
 });
+
+Deno.test("generateKeyPair promisify", async () => {
+  const passphrase = "mypassphrase";
+  const cipher = "aes-256-cbc";
+  const modulusLength = 4096;
+
+  const { privateKey, publicKey } = await promisify(generateKeyPair)("rsa", {
+    modulusLength,
+    publicKeyEncoding: {
+      type: "spki",
+      format: "pem",
+    },
+    privateKeyEncoding: {
+      type: "pkcs8",
+      format: "pem",
+      cipher,
+      passphrase,
+    },
+  });
+
+  assert(publicKey.startsWith("-----BEGIN PUBLIC KEY-----"));
+  assert(privateKey.startsWith("-----BEGIN PRIVATE KEY-----"));
+});