NextAuth.js

import NextAuth from "next-auth";
import GoogleProvider from "next-auth/providers/google";
import CredentialsProvider from "next-auth/providers/credentials";

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;
  }
}

export const authOptions = {
  providers: [
    CredentialsProvider({
      async authorize(credentials) {
        if (await isDisposable(credentials.email)) {
          throw new Error("Please use a real email address.");
        }
        // ...your auth logic
        return { id: "1", email: credentials.email };
      },
    }),
  ],
};