https://github.com/paypay/paypayopa-sdk-node/blob/646a420f6e61f65cfd4855f355d21de95af5fef8/src/lib/paypay-rest-sdk.ts#L31 を動くようにしたやつ

paypay-auth-generator.ts

import CryptoJS from 'crypto-js';
import {v4 as uuidv4 } from "uuid"

// https://github.com/paypay/paypayopa-sdk-node/blob/646a420f6e61f65cfd4855f355d21de95af5fef8/src/lib/paypay-rest-sdk.ts#L31
// ↑ここから引っ張ってきてとりあえず動くっぽい感じにしたやつ
export const createAuthHeader = (method: string, resourceUrl: string, payLoad: any, auth: any) => {
    let AUTH_TYPE = "hmac OPA-Auth";
    const epoch = Math.ceil(Date.now() / 1000); // ミリ秒を削る必要アリ
    let contentType = 'application/json';
    const nonce	= uuidv4().slice(0,8);
    let bodyHash = "";
    if (method == "GET" || !payLoad) {
      payLoad = "";
      bodyHash = "empty";
      contentType = "empty";
      console.log(`coming inside GET`);
    } else {
      let md5 = CryptoJS.algo.MD5.create();
      md5.update(contentType);
      md5.update(JSON.stringify(payLoad)); // JSON stringifyする必要アリ
      bodyHash = md5
        .finalize()
        .toString(CryptoJS.enc.Base64)
        .toString("utf-8");
    }
    let pathfinder = resourceUrl.split("?");
    resourceUrl = pathfinder[0];
    let signatureRawData = [resourceUrl, method, nonce, epoch, contentType, bodyHash].join("\n");
    let hash = CryptoJS.HmacSHA256(signatureRawData, auth[1]);
    let hashInBase64 = encodeURI(CryptoJS.enc.Base64.stringify(hash));
    
    let header = [auth[0], hashInBase64, nonce, epoch, bodyHash].join(":");
    return AUTH_TYPE + ":" + header;
  }

usage.ts

const API_KEY = process.env.API_KEY
const API_SECRET = process.env.API_SECRET
const payload = {
  merchantPaymentId: 'my_payment_id',
  amount: {
    amount: 1,
    currency: 'JPY',
  },
  codeType: 'ORDER_QR',
  orderDescription: "Mune's Favourite Cake",
  isAuthorization: false,
  redirectUrl: 'https://paypay.ne.jp/',
  redirectType: 'WEB_LINK',
  userAgent: 'Mozilla/5.0 (iPhone; CPU iPhone OS 10_3 like Mac OS X) AppleWebKit/602.1.50 (KHTML, like Gecko) CriOS/56.0.2924.75 Mobile/14E5239e Safari/602.1'
}
const apiBase = "https://stg-api.paypay.ne.jp"
const createQrCode = "/v2/codes"
const auth = [
  API_KEY, 
  API_SECRET,
]
const header = createAuthHeader("POST", createQrCode, payload,auth)

axios.post(`${apiBase}${createQrCode}`,payload, {
  headers: {
    "Authorization":`${header}`,
    'Content-Type': 'application/json' // content type指定
  }
}).catch(e => {
  console.log(e.response.data)
}).then(r => {
  console.log(r)
})