编辑app.js文件，就是做微信后台验证,启动服务器;

var Koa=require("koa");
var sha1=require("sha1");
var config = {
    wechat:{
        appID:"*****",
        appSecret:"*****",
        token:"******"
    }
}
var app= new Koa();

app.use(function *(next){
    var token=config.wechat.token;
    var signature=this.query.signature;
    var nonce=this.query.nonce;
    var timestamp=this.query.timestamp;
    var echostr=this.query.echostr;
    var str=[token,timestamp,nonce].sort().join("");
    var sha=sha1(str);
    console.log("this.query");
    console.log(this.query);

    if(sha===signature){
        this.body=echostr+"";
    }else{
        this.body="wrong";
    }
})
app.listen(8080);
console.log("START WECHAT SERVER AT PORT 8080");