如何使用async和await這對組合設計統一的取Access Token的函數

最近我在使用SAP雲平台的機器學習API做和SAP系統的內建，因為SAP Cloud Platform Leonardo上的機器學期API，每次消費時需要傳一個Access Token，故在每次實際調用API前，我需要先發一個請求去擷取Access Token. 該請求的響應，除了傳回實際的token外，還有一個過期時間，expires_in字段：

我的代碼如下：

const request = require('request-promise-native');

var config = require('../config.js');
 
var TOKEN = undefined;
var EXPIRES_IN = undefined;
var TOKEN_FETCHED_SINCE = undefined;


function isCurrentDateExpired(){
    var current = new Date();

    var diffInMilliSeconds = current - TOKEN_FETCHED_SINCE;
    var diffInSecond = Math.ceil(diffInMilliSeconds/1000);
    var expired = diffInSecond >= EXPIRES_IN ? true:false;
    // for debug;
    // expired = true; 
    return expired;
}

async function getAccessToken(){
    if( TOKEN === undefined || isCurrentDateExpired()){
        var raw = new Buffer(config.username + ":" + config.password);
        const accessToken = await request({
            method: 'GET',
            headers: {
                'Authorization': 'Basic ' + raw.toString('base64')
            },
            url: config.ACCESS_TOKEN,
            json: false
        });
        var oToken = JSON.parse(accessToken);
        EXPIRES_IN = oToken.expires_in;
        TOKEN = oToken.access_token;
        TOKEN_FETCHED_SINCE = new Date();
        return oToken.access_token;
    }
    else{
        return TOKEN;
    }
}

var request1 = getAccessToken();
var freshNewToken, secondTimeToken;

request1.then(function(o){
    // console.log("token1: " + o);
     freshNewToken = o;
});

function test2(){
    var b = getAccessToken();
    b.then(function(o){
    // console.log("token2: " + o);
        secondTimeToken = o;
        console.log("they should be equal: " + (freshNewToken == secondTimeToken));
    });
}

setTimeout( test2, 6000);