.gitignore

node_modules

package-lock.json

{
  "name": "work",
  "version": "1.0.0",
  "lockfileVersion": 1,
  "requires": true,
  "dependencies": {
    "base64url": {
      "version": "3.0.1",
      "resolved": "https://registry.npmjs.org/base64url/-/base64url-3.0.1.tgz",
      "integrity": "sha512-ir1UPr3dkwexU7FdV8qBBbNDRUhMmIekYMFZfi+C/sLNnRESKPl23nB9b2pltqfOQNnGzsDdId90AEtG5tCx4A=="
    },
    "js-sha256": {
      "version": "0.9.0",
      "resolved": "https://registry.npmjs.org/js-sha256/-/js-sha256-0.9.0.tgz",
      "integrity": "sha512-sga3MHh9sgQN2+pJ9VYZ+1LPwXOxuBJBA5nrR5/ofPfuiJBE2hnjsaN8se8JznOmGLN2p49Pe5U/ttafcs/apA=="
    }
  }
}

package.json

{
  "name": "work",
  "version": "1.0.0",
  "description": "",
  "main": "pkce.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "base64url": "^3.0.1",
    "js-sha256": "^0.9.0"
  }
}

pkce.js

"use strict";
const base64url = require("base64url");
const sha256 = require("js-sha256");
// 参考: https://tools.ietf.org/html/rfc7636#appendix-B
(async () => {
  const code_verifier = get_code_verifier();
  const code_challenge = get_code_challenge(code_verifier);
  console.log(
    `code_verifier = ${code_verifier}\nのとき\ncode_challenge = ${code_challenge}\nです`
  );
})();

function get_code_challenge(str) {
  const hash = sha256.arrayBuffer(str);
  return base64url(hash);
}
function get_code_verifier() {
  let buf = Buffer.alloc(32);
  for (let i = 0; i < buf.length; i++) {
    const random_num = Math.floor(Math.random() * 256);
    buf.writeUInt8(random_num, i);
  }
  return base64url(buf);
}