Cypress load environment variables in custom commands

[janhesters]

I'm building a Next.js app and write my tests using Cypress. I configure the environment variables using a .env.local file locally.
I'm trying to write a custom command in Cypress that encrypts a session in cypress/support/command.ts.

import { encryptSession } from 'utils/sessions';

Cypress.Commands.add(
  'loginWithCookie',
  ({
    issuer = 'some-issuer',
    publicAddress = 'some-address',
    email = 'some-mail',
  } = {}) => {
    const session = { issuer, publicAddress, email };

    return encryptSession(session).then(token => {
      cy.setCookie('my-session-token', token);
      return session;
    });
  },
);

When this command runs, it fails because encryptSession uses a TOKEN_SECRET environment variable, that Cypress doesn't load.

import Iron from '@hapi/iron';

const TOKEN_SECRET = process.env.TOKEN_SECRET || '';

export function encryptSession(session: Record<string, unknown>) {
  return Iron.seal(session, TOKEN_SECRET, Iron.defaults);
}

How can I get Cypress to load the environment variables from that file, if its runs locally (and from the CI's env key in the .yaml file if its in the CI)?