Allow custom transports for nodemailer

[alfonsodev]

Description 📓

Many email providers recommend using their APIs instead of SMTP,
Nodemailer allows to use custom transports and there are plenty already implemented,
for example nodemailer-sendgrid-transport.

This is how I was expecting it would work:

import NextAuth from "next-auth";
import EmailProvider from "next-auth/providers/email";
import sgTransport from "nodemailer-sendgrid-transport";

const server = sgTransport({
  auth: {
    api_user: process.env.SENDGRID_API_USER,
    api_key: process.env.SENDGRID_API_KEY
  },
});

export default NextAuth({
  providers: [
    EmailProvider({
      server,
      from: "foo@bar.com",
    }),
  ],
});

How to reproduce ☕️

does not apply

Contributing 🙌🏽

Yes, I am willing to help implement this feature in a PR

[atuttle]

I would also very much like to see this implemented, but my timeline probably doesn't have enough room to wait for a community/ @nextauthjs org solution. @alfonsodev by any chance have you already implemented this in a fork or anything?

There are lots of great reasons to use something other than SMTP. Some mail services don't even offer SMTP. Perhaps you want to log transactional emails like these, so you already have an API for transactional email sending that you want to make use of. Seems like something that would be very beneficial to add.

[dextermb]

How's this looking? Has anyone contributed to implement this yet?

[blaine]

I'm not sure if it's expected, but this would work today, EXCEPT that there's a bug in the core/auth provider that expects attributes that only the SMTP transport provides.

This is a very tricky thing to build a public & reproducible test case for, and I don't have the time to do it (I've already spent enough time on this!! ;-) ), but this (automatically closed) bug report details the issue and the fix/workaround:

#9387

For reference, the following code snippet (modulo the omitted html() and text() functions) is a functional implementation using the nodemailer mailgun transport.

import Email from '@auth/core/providers/email';
import mg from 'nodemailer-mailgun-transport';
import { createTransport } from 'nodemailer';

Email({
  from: env.AUTH_MAILGUN_FROM,
  server: mg({
	auth: {
		api_key: env.AUTH_MAILGUN_API_KEY,
		domain: env.AUTH_MAILGUN_DOMAIN
	}
}),
  allowDangerousEmailAccountLinking: true,
  sendVerificationRequest: async ({ identifier, url, provider, theme }) => {
	const { host } = new URL(url);
	// NOTE: You are not required to use `nodemailer`, use whatever you want.
	const transport = createTransport(provider.server);
	const result = await transport.sendMail({
		to: identifier,
		from: provider.from,
		subject: `Sign in to ${host}`,
		text: text({ url, host }),
		html: html({ url, host, theme })
	});
	if (!result.messageId) {
		throw new Error(`Email could not be sent`);
	}
}
})

Hopefully that's useful to someone!

Just in case anyone comes looking for the error message:

const failed = result.rejected.concat(result.pending).filter(Boolean);
TypeError: Cannot read properties of undefined (reading 'concat')