如何使用async和await这对组合设计统一的取Access Token的函数

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);