Nextjs HOC to deal with authentication for SSR and CSR pages

nextjs-ssr-csr-auth-hoc.js

import React from 'react';
import { Router } from 'next-router';

import getAuthSession from 'services/authSession';

function redirect(res) {
  if (res) {
    // SSR
    res.writeHead(302, { Location: '/' });
    res.end();
  } else {
    // Client side
    Router.push('/');
  }
}

export default (Component, { loggedOnly = false } = {}) => {
  const withAuthSession = props => {
    return <Component {...props} />;
  };

  withAuthSession.getInitialProps = async ctx => {
    let authSession;

    if (ctx.req) {
      // SSR
      authSession = ctx.req.authSession;
    } else {
      // Client side
      const [, response] = await getAuthSession();
      authSession = response.data.authSession;
    }

    if (loggedOnly && !authSession.profile) {
      redirect(ctx.res);
    }
    
    let componentProps = {};
    if (Component.getInitialProps) {
      componentProps = await Component.getInitialProps(ctx);
    }

    return { authSession, ...componentProps };
  };

  return withAuthSession;
};

where are getAuthSession code ?