Auth.js / NextAuth: Custom Email Provider with AutoSend REST API for passwordless magic links

API & SMTP Integration
1

How do you implement a custom Email Provider in Auth.js (NextAuth v5) using AutoSend’s REST API to render clean branded HTML magic links?

2

Auth.js (NextAuth v5) Custom Email Provider with AutoSend

Instead of relying on heavy nodemailer transports, you can use Auth.js’s sendVerificationRequest callback to trigger AutoSend via native fetch.

// auth.ts (Auth.js v5 / NextAuth)
import NextAuth from "next-auth";
import EmailProvider from "next-auth/providers/email";

export const { handlers, auth, signIn, signOut } = NextAuth({
  providers: [
    EmailProvider({
      server: {}, // Bypass default nodemailer
      from: "Auth Desk <auth@yourdomain.com>",
      async sendVerificationRequest({ identifier: email, url, provider }) {
        const res = await fetch("https://api.autosend.com/v1/mails/send", {
          method: "POST",
          headers: {
            "Authorization": `Bearer ${process.env.AUTOSEND_API_KEY}`,
            "Content-Type": "application/json",
          },
          body: JSON.stringify({
            from: provider.from,
            to: [email],
            subject: "Sign in to your account",
            html: `
              <div style="font-family: sans-serif; padding: 24px; color: #111;">
                <h2>Welcome Back</h2>
                <p>Click the secure link below to sign in:</p>
                <p><a href="${url}" style="background: #00B95C; color: #fff; padding: 12px 20px; border-radius: 6px; text-decoration: none; display: inline-block;">Sign In</a></p>
                <p style="color: #666; font-size: 13px;">This link will expire in 24 hours.</p>
              </div>
            `,
          }),
        });

        if (!res.ok) {
          const err = await res.json().catch(() => ({ message: "Unknown error" }));
          throw new Error(`AutoSend verification email failed: ${JSON.stringify(err)}`);
        }
      },
    }),
  ],
});

Relevant Documentation