sf_login.ts

import * as crypto from "crypto";
import fetch, { Headers } from "node-fetch";
import { promisify } from "util";

const pbkdf2 = promisify(crypto.pbkdf2);

const endpoint = "https://sync.standardnotes.org";
const email = process.env.SN_EMAIL || "";
const uip = process.env.SN_PASSWORD || "";

interface AuthParamsResponse {
  identifier: string;
  pw_salt: string;
  pw_cost: number;
  pw_nonce: string;
  version: string;
  pw_func: string;
  pw_alg: string;
  pw_key_size: number;
}

async function login(): Promise<void> {
  const {
    pw_cost,
    pw_nonce,
    version
  }: AuthParamsResponse = await fetch(
    `${endpoint}/auth/params?email=${email}`
  ).then(res => res.json());

  const salt = crypto
    .createHash("sha256")
    .update([email, "SF", version, pw_cost, pw_nonce].join(":"), "utf8")
    .digest()
    .toString("hex");

  const key = (await pbkdf2(uip, salt, pw_cost, 768, "sha512")).toString("hex");

  const splitLength = key.length / 3;

  const pw = key.slice(0, splitLength);
  // const mk = key.slice(splitLength, splitLength * 2);
  // const ak = key.slice(splitLength * 2, splitLength * 3);

  const token = await fetch(`${endpoint}/auth/sign_in`, {
    method: "POST",
    headers: new Headers({
      "Content-Type": "application/json"
    }),
    body: JSON.stringify({
      password: pw,
      email: "mail@mathiswiehl.de"
    })
  }).then(res => res.json());

  console.log(token);
}

login().catch(console.error);

Sounds good. PS I don't get notified of comments inside gists or commits for whatever reason. So be sure to update the original issue if you come across any other issues.