Next.js reach .env from /lib without exposing to the client

I my next.js blog app I have been trying to setup a global API call:

import { createClient } from "contentful";

const client = createClient({
  space: process.env.CONTENTFUL_SPACE_ID,
  accessToken: process.env.CONTENTFUL_ACCESS_KEY,
});

const auth_data = await client.getEntries({ content_type: "author" });

export function getAuthors() {
  var authors = [];

  var auth_len = auth_data.items.length;
  for (var i = 0; i < auth_len; i++) {
    authors.push({
      authorSlug: auth_data.items[i].fields.name
        .toString()
        .replace(/ /g, "-")
        .toLowerCase(),
      authorContent: auth_data.items[i].fields.description,
      authorFrontMatter: {
        title: auth_data.items[i].fields.name,
        image: "https:" + auth_data.items[i].fields.image.fields.file.url,
      },
    });
  }
  return authors;
}

I keep getting TypeError: Expected parameter accessToken because the environment variable will not be reached from the /lib foleder where this getAuthor() function is located. If I prefix the variable with NEXT_PUBLIC_ I could reach the environment variable from the /lib, but at the same time I would expose the variables to the browser.

Is there a way to reach the environment variable from the /lib WITHOUT exposing them to the browser?