wx.login(object,object)
//index.jsPage ({data: {openid: null,session_key: null,unionid: null,},onLoad () {wx.login ({success: res => {if (res.code) {wx.request ({url: '/onLogin', //测试apidata: {code: res.code, //用户登录凭证，有效期5分钟},header: {'content-type': 'application/json', //请求头},success: function (result) {//json转化const res = JSON.parse (result);//解构赋值const {openid, session_key, unionid, errorcode} = res.data;//errorcode 状态码if (errorcode === -1) {console.log ('系统繁忙，请稍微重试');return;} else if (errorcode === 0) {console.log ('请求成功');} else if (errorcode === 40029) {console.log ('code无效');return;} else if (errorcode === 45011) {console.log ('请求过于频繁');return} else {console.log ('未知错误');return }//data存储this.data.openid = openid;this.data['session_key'] = session_key;this.data.unionid = unionid;//数据缓存this.setStorage ({key: 'WxLoginInfo',value: {openid: openid,session_key: session_key,unionid: unionid,},});},fail: function (result) {console.log (result);},});} else {console.log ('登录失败' + res.errMsg);}},});},});
从请求登录到返回成功经历了以下几个过程：
1.通过wx.login获取用户登录凭证res.code
2.把res.code通过wx.request发送到后台换取session_key和openid
3.session_key是会话秘钥，openid是用户标识符，为了保证安全,session_key不应该下发到小程序中。
