Block disposable email signups in Astro

The code

// src/pages/api/signup.ts
import type { APIRoute } from 'astro';

async function isDisposable(email: string) {
  const r = await fetch(
    `https://api.checkdisposable.email/v1/check?email=${encodeURIComponent(email)}`,
    { headers: { Authorization: `Bearer ${import.meta.env.CDE_KEY}` } }
  );
  if (!r.ok) return false;
  return (await r.json()).is_disposable === true;
}

export const POST: APIRoute = async ({ request }) => {
  const form = await request.formData();
  const email = String(form.get('email') ?? '');

  if (await isDisposable(email)) {
    return new Response(
      JSON.stringify({ error: 'Please use a real email address.' }),
      { status: 400, headers: { 'content-type': 'application/json' } }
    );
  }

  return new Response(JSON.stringify({ ok: true }), {
    headers: { 'content-type': 'application/json' },
  });
};

Notes

Enable SSR or hybrid

Set `output: "server"` (or `"hybrid"` and `export const prerender = false` on this route) in astro.config.mjs. Endpoints don't run in fully static builds.

Auth: Better Auth or Clerk

Most Astro signup flows wrap Better Auth or Clerk. Drop the check before calling their signup function — the endpoint stays the same.

Edge-compatible

The handler uses only standard fetch — runs unchanged on Cloudflare, Vercel, Deno, or Netlify edge adapters.