webToAlbum:function(e) {
    wx.getSetting({
      withSubscriptions: true,
      success:function(res){
        if(!res.authSetting['scope.writePhotosAlbum'])
        {
          wx.authorize({
            scope: 'scope.writePhotosAlbum',
            success:function(){ 
              wx.showToast({
                title: '授权成功！',
                duration:2000
              });
            },
            fail:function(){
              wx.showToast({
                title: '授权失败',
                duration:2000
              })
            }
          })
        }
        else
        {
          wx.showToast({
            title: '已经授权',
            duration:2000,
            icon:'success'
          })
        }
      },
      fail:function(){
        wx.showToast({
          title: '打开授权失败',
          duration:2000,
          icon:'error'
        })
      }
    })
  },

我本意是：每次运行都要弹窗提示是否允许。但它这个好像只要一次授权，以后就不用授权了，怎么取消这个授权有效呢？谢谢