Integre faturação certificada no seu sistema

// Config (do seu .env)
const BASE = "https://nexainvoice.nexamakers.pt";
const CLIENT_ID = process.env.NEXAINVOICE_CLIENT_ID;
const CLIENT_SECRET = process.env.NEXAINVOICE_CLIENT_SECRET;
const REDIRECT_URI = "https://oseusistema.pt/oauth/nexainvoice/callback";

// 1) Iniciar a ligacao — redirecionar o utilizador para autorizar
app.get("/ligar-nexainvoice", (req, res) => {
  const state = crypto.randomBytes(16).toString("hex");
  req.session.nxiState = state;                 // guardar p/ validar no callback
  const url = new URL(BASE + "/oauth/authorize");
  url.searchParams.set("response_type", "code");
  url.searchParams.set("client_id", CLIENT_ID);
  url.searchParams.set("redirect_uri", REDIRECT_URI);
  url.searchParams.set("state", state);
  res.redirect(url.toString());
});

// 2) Callback — trocar o code por um access_token
app.get("/oauth/nexainvoice/callback", async (req, res) => {
  if (req.query.state !== req.session.nxiState) return res.status(400).send("state invalido");
  const r = await fetch(BASE + "/api/oauth/token", {
    method: "POST",
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify({
      grant_type: "authorization_code",
      code: req.query.code,
      client_id: CLIENT_ID,
      client_secret: CLIENT_SECRET,
      redirect_uri: REDIRECT_URI,
    }),
  });
  const { access_token, company } = await r.json();
  // guardar access_token associado a esta empresa/cliente
  res.redirect("/definicoes?ligado=1");
});

// 3) Emitir uma fatura
async function emitirFatura(accessToken) {
  const r = await fetch(BASE + "/api/v1/invoices", {
    method: "POST",
    headers: { "Authorization": "Bearer " + accessToken, "Content-Type": "application/json" },
    body: JSON.stringify({
      type: "FT",
      customer: { name: "Cliente Lda", nif: "509112233" },
      lines: [{ description: "Servico", quantity: 1, unitPrice: 100, vatRate: 23 }],
    }),
  });
  return (await r.json()).invoice;   // { docNo, atcud, ... }
}