Using fetch with basic auth

fetch-basic-auth.md

let username = 'john';
let password = 'doe';
let url = `https://httpbin.org/basic-auth/${username}/${password}`
let authString = `${username}:${password}`
let headers = new Headers();
headers.set('Authorization', 'Basic ' + btoa(authString))
fetch(url,{method: 'GET', headers: headers})
    .then(function (response) {
        console.log (response)
        return response
    });

"btoa is not defined" when this code gets used in a Node14 lambda on AWS.