Opens a login window popup in the center of the screen using window.open().

openAuthPopupInScreenCenter.js

const popupWidth = 400;
const popupHeight = 600;
// Maths "borrowed" from the smart folks at Auth0 (https://github.com/auth0/auth0-spa-js/blob/451956f5615bdd7e8fe3c313dbe30d1e31b855f1/src/utils.ts#L92)
const popupLeft = window.screenX + (window.innerWidth - popupWidth) / 2;
const popupTop = window.screenY + (window.innerHeight - popupHeight) / 2;
// The window.open call needs to be called inside an event listener for a user-created action like a click
document.addEventListener("click", ()=>window.open("https://exmaple.com?in_popup=ye", "my-auth-popup", `popup,width=${popupWidth},height=${popupHeight},left=${popupLeft},top=${popupTop}`));