Fastify (Node.js)

const fastify = require('fastify')({ logger: true })

async function isDisposable(email) {
  try {
    const r = await fetch(
      `https://api.disposableguard.com/v1/check?email=${encodeURIComponent(email)}`,
      { headers: { Authorization: `Bearer ${process.env.DG_KEY}` } }
    )
    if (!r.ok) return false
    const data = await r.json()
    return data.is_disposable === true
  } catch {
    return false
  }
}

fastify.post('/signup', async (request, reply) => {
  const { email, password } = request.body

  if (await isDisposable(email)) {
    return reply.code(400).send({ error: 'Please use a real email address.' })
  }

  // ...signup logic
  return { ok: true }
})

fastify.listen({ port: 3000 })