Server-action sign-in
A Next.js server action performs email authentication and must persist the resulting session cookie.
Better Auth · Function
nextCookies
nextCookies is a Better Auth plugin for Next.js server actions. It automatically applies authentication cookies emitted through Set-Cookie response headers.
How it works
The nextCookies plugin integrates Better Auth with Next.js server actions. It watches authentication responses and uses Next.js cookie handling to apply any Set-Cookie headers automatically, allowing operations such as email sign-in or sign-up to establish cookies without manually calling the Next.js cookies helper.
Syntax
nextCookies()Key points
- Use the plugin when Better Auth calls run in Next.js server actions and need to persist authentication cookies.
- Cookie synchronization is triggered by a
Set-Cookieresponse header. - After installation, cookie-setting Better Auth functions update the Next.js cookie store without extra cookie code.
- Typical affected calls include email sign-in and email sign-up invoked from server actions.
Common mistakes
- Place
nextCookies()last in the Better Auth plugin array; the documentation explicitly requires that ordering.
Example: Enable nextCookies in Next.js
import { betterAuth } from "better-auth";
import { nextCookies } from "better-auth/next-js";
export const auth = betterAuth({
plugins: [nextCookies()],
});Register the plugin last in the Better Auth plugin list so server actions can apply cookies emitted by authentication responses.
When to use it
Server-action sign-up
A Next.js server action creates an account and needs the new authentication state stored in cookies.
Automatic response-cookie handling
An application wants response cookies from Better Auth API calls bridged into Next.js cookie handling without custom plumbing.
Interview questions
QWhat problem does nextCookies solve?
It is a Next.js integration plugin for Better Auth server actions. It automatically applies cookies whenever an authentication response includes a Set-Cookie header.
Follow-up: Why is plugin order relevant? The documented configuration requires this plugin to be last, so later plugins do not interfere with its response-cookie handling.
QWhy is this needed in a server action?
Next.js server actions do not automatically set cookies from Better Auth responses because cookie mutation must use Next.js's cookies helper. The plugin handles that integration automatically.
Follow-up: Which operations benefit? Server-side operations that need to establish or update authentication cookies, such as email sign-in and sign-up.
QHow do you configure it?
Import nextCookies from better-auth/next-js, call it in the plugins array, and put it at the end of that array. After that, cookie-setting authentication calls can update cookies automatically.
Follow-up: What should remain separate? Middleware or proxy session checks should not be treated as full session validation; protected actions still require server-side validation.
Related
signInEmailsignUpEmailgetSessionCookiebetterAuth