I had this problem. My app depended on cookies for authentication, and using Next.js apparently my cookies were not set on first page initialization.

I had this code, which was in charge of hitting a GET endpoint using Axios:

Bookings.getInitialProps = async ctx => {
  const response = await axios.get('http://localhost:3000/api/bookings/list')

  return {
    bookings: response.data
  }
}

I had Passport.js on the server side endpoint, but it failed to authenticate the user on the SSR page, because it didn’t find any cookie.

I had to change my code to this, adding the cookies to the headers:

Bookings.getInitialProps = async ctx => {
  const response = await axios({
    method: 'get',
    url: 'http://localhost:3000/api/bookings/list',
    headers: ctx.req ? { cookie: ctx.req.headers.cookie } : undefined
  })

  return {
    bookings: response.data
  }
}

The key to making cookies available in the backend was adding:

headers: ctx.req ? { cookie: ctx.req.headers.cookie } : undefined

to the Axios configuration.

Lessons in this unit:

0:	Introduction
1:	Getting started with Next.js (Pages Router), a tutorial
2:	How to install Next.js
3:	How I set up a Next.js project structure
4:	Linking two pages in Next.js using Link
5:	How to use the Next.js Router
6:	Dynamic content in Next.js with the router
7:	Prefetching content in Next.js
8:	How to programmatically change a route in Next.js
9:	View source to confirm SSR is working in Next.js
10:	Feed data to a Next.js component using getInitialProps
11:	Styling Next.js components using CSS
12:	Next.js: populate the head tag with custom tags
13:	How to use Next.js API Routes
14:	▶︎ How to get cookies server-side in a Next.js app
15:	Deploying a Next.js application on Now
16:	Deploying a Next.js app in production