Beego处理后在中间件中获得响应主体

Question

I have to append parameter in JSON response after request processing is completed and before sending. I can do in after exec filter. Here I defined filter like this,

beego.InsertFilter("*", beego.AfterExec, AddRequestAfterExec, false)

Now in this AddRequestAfterExec method, I am unable to read JSON response. I need to read JSON response and add parameter to it. I searched many things, but did not find any thing useful. So far I have left it empty.

func AddRequestAfterExec(c *context.Context) {}

Can anybody help, how to read Response in this function and modify it?

Also I am sending response from API controller like this

authController.ServeJSON()