Auth.js

coss/authjs is an email provider for Auth.js (NextAuth.js v5 and the other @auth/* frameworks). It sends Auth.js's magic sign-in links through coss.com.

npm install coss next-auth@beta

export const { handlers, auth, signIn, signOut } = NextAuth({
  adapter, // email sign-in stores its tokens, so it needs a database adapter
  providers: [Coss({ from: "Acme <auth@acme.com>" })],
});

Set AUTH_COSS_KEY (Auth.js's naming for a provider's key) or COSS_API_KEY, or pass apiKey. Sign in with signIn("coss", { email }).

Options

Coss({
  from: "Acme <auth@acme.com>",
  maxAge: 24 * 60 * 60, // how long a link works, in seconds (the default)
  name: "Email", // the button label on Auth.js's sign-in page
  render: ({ url, host }) => ({
    subject: `Sign in to ${host}`,
    html: `<a href="${url}">Sign in</a>`,
    text: `Sign in to ${host}: ${url}`,
  }),
});

Without render, the email is Auth.js's own sign-in email, in your theme's brand color.

Behaviour

• Links go out with category: "account" and open and click tracking off.
• The idempotency key is a hash of the link's token, so a retried request sends the link once.
• When coss.com refuses the email, sendVerificationRequest throws a CossSendError, which fails the sign-in attempt.