AI app sign-in checks

// GET /ai-sign-in?gr_request=… → your AI app sign-in address
//
// When someone connects ChatGPT, Claude or another AI app to their account,
// the installation sends them here. This route signs them in, reads the
// request, checks they belong to its account, asks them to confirm, and sends
// them back. Set its address in Platform › What customers get › Developers ›
// AI app sign-in address.
//
//   GORUNNER_URL=https://automations.example.com GORUNNER_EMBED_KEY=gre_… node ai-sign-in.mjs
import { randomBytes } from "node:crypto"
import { createServer } from "node:http"

const GORUNNER_URL = process.env.GORUNNER_URL // the installation's web address
const GORUNNER_EMBED_KEY = process.env.GORUNNER_EMBED_KEY // Platform › Partner keys
const PORT = Number(process.env.PORT || 3000)

// Who is signed in to your app, for this request. Replace this with your own
// session lookup: your id for the person and their role. Answer null when
// nobody is signed in; this route then sends them to your sign-in page first.
function signedIn(req) {
  return { user: { id: "ada-123", name: "Ada Lovelace", email: "ada.lovelace@example.com" }, role: "editor" }
}

// Whether that person belongs to the customer account the request is for
// (your id for it). Replace this with your own check.
function belongsTo(login, accountId) {
  return accountId === "acct-bakery"
}

const EXPIRED = "This connection request has expired. Go back to your AI app and connect again."
const esc = (s) => String(s).replace(/[&<>"']/g, (c) => `&#${c.charCodeAt(0)};`)

async function gorunner(method, path, body) {
  const answer = await fetch(`${GORUNNER_URL}/api/embed/v1/oauth-requests/${path}`, {
    method,
    headers: { Authorization: `Bearer ${GORUNNER_EMBED_KEY}`, "Content-Type": "application/json" },
    body: body && JSON.stringify(body),
  })
  return { status: answer.status, body: await answer.json().catch(() => ({})) }
}

function page(res, status, html, headers = {}) {
  res.writeHead(status, {
    "Content-Type": "text/html; charset=utf-8",
    "Content-Security-Policy": "frame-ancestors 'none'",
    "X-Frame-Options": "DENY",
    "Referrer-Policy": "no-referrer",
    "Cache-Control": "no-store",
    ...headers,
  })
  res.end(`<!doctype html><meta charset="utf-8"><title>Connect an AI app</title>${html}`)
}

// Only ever to the continueUrl the installation answered, on its own origin.
function goBack(res, answer) {
  const to = answer.body.data?.continueUrl ?? answer.body.error?.details?.continueUrl
  if (answer.status === 404 && !to) return page(res, 404, `<p>${EXPIRED}</p>`)
  if (!to || new URL(to).origin !== new URL(GORUNNER_URL).origin) return page(res, 502, "<p>Something went wrong. Go back to your AI app and try again.</p>")
  res.writeHead(303, { Location: to, "Cache-Control": "no-store", "Referrer-Policy": "no-referrer" }).end()
}

createServer(async (req, res) => {
  const url = new URL(req.url, "http://localhost")
  if (url.pathname !== "/ai-sign-in") return page(res, 404, "<p>Not found</p>")
  const login = signedIn(req)
  if (!login) return res.writeHead(303, { Location: `/sign-in?next=${encodeURIComponent(req.url)}` }).end()
  const cookie = /(?:^|;\s*)ai_csrf=([\w-]+)/.exec(req.headers.cookie || "")?.[1]

  try {
    if (req.method === "GET") {
      // 1. Signed in. 2. Now read the request: its account comes from the installation, never from this link.
      const id = url.searchParams.get("gr_request") || ""
      const request = await gorunner("GET", encodeURIComponent(id))
      if (request.status !== 200) return goBack(res, request)
      const { account, client } = request.body.data
      // 3. The person must belong to that account.
      if (!belongsTo(login, account.id)) return goBack(res, await gorunner("POST", `${encodeURIComponent(id)}/deny`, { reason: "not_member" }))
      // 4. Ask, every time, even when they were already signed in.
      const csrf = cookie || randomBytes(32).toString("base64url")
      return page(
        res,
        200,
        `<h1>Connect ${esc(client.name)} (${esc(client.redirectHost)}) to ${esc(account.name)}?</h1>
<p>You’ll choose what it may do on the next page.</p>
<form method="post"><input type="hidden" name="request" value="${esc(id)}"><input type="hidden" name="csrf" value="${csrf}">
<button name="answer" value="cancel">Cancel</button> <button name="answer" value="continue">Continue</button></form>`,
        { "Set-Cookie": `ai_csrf=${csrf}; Path=/ai-sign-in; HttpOnly; SameSite=Strict` },
      )
    }

    if (req.method === "POST") {
      let raw = ""
      for await (const chunk of req) raw += chunk
      const form = new URLSearchParams(raw)
      // Only a form this route drew: the same origin, and the CSRF value it set.
      // (Under Referrer-Policy: no-referrer the browser sends Origin: null; Sec-Fetch-Site then decides.)
      const origin = req.headers.origin !== "null" && req.headers.origin
      const sameOrigin = origin ? origin.replace(/^https?:\/\//, "") === req.headers.host : req.headers["sec-fetch-site"] === "same-origin"
      if (!sameOrigin || !cookie || form.get("csrf") !== cookie) return page(res, 403, "<p>Forbidden</p>")
      const id = encodeURIComponent(form.get("request") || "")
      // Read the request again: the account is the installation's, not the form's.
      const request = await gorunner("GET", id)
      if (request.status !== 200) return goBack(res, request)
      const { account } = request.body.data
      if (form.get("answer") !== "continue" || !belongsTo(login, account.id)) {
        return goBack(res, await gorunner("POST", `${id}/deny`, { reason: form.get("answer") === "continue" ? "not_member" : "cancelled" }))
      }
      // 5. Continue: the person, their role, and the account from step 2.
      return goBack(res, await gorunner("POST", `${id}/complete`, { user: login.user, account, role: login.role, provision: false }))
    }
    page(res, 405, "<p>Method not allowed</p>")
  } catch (e) {
    console.error("AI app sign-in failed:", e.message) // never log a continueUrl: it carries a one-use ticket
    page(res, 502, "<p>Something went wrong. Go back to your AI app and try again.</p>")
  }
}).listen(PORT)