Firebase Auth

// functions/src/blockDisposable.js
const functions = require("firebase-functions/v2");
const admin = require("firebase-admin");
admin.initializeApp();

exports.beforeUserCreated = functions.identity.beforeUserCreated(
  async (event) => {
    const { email } = event.data;
    if (!email) return;

    try {
      const r = await fetch(
        `https://api.disposableguard.com/v1/check?email=${encodeURIComponent(email)}`,
        {
          headers: {
            Authorization: `Bearer ${process.env.DG_KEY}`,
          },
        }
      );
      if (r.ok) {
        const data = await r.json();
        if (data.is_disposable) {
          throw new https.HttpsError(
            "invalid-argument",
            "Please use a real email address."
          );
        }
      }
    } catch (e) {
      if (e.code) throw e;
      // fail-open
    }
  }
);