node.js – 是否可以获取快速路由器的基本URL

var express = require('express');
var app = express();

// This will work just fine
app.use('/',getAuthRouter());

// The redirects here will end up going to /oauth/callBACk 
//    instead of /admin/oauth/callBACk
app.use('/admin',getAuthRouter());

function getAuthRouter() {
  var authRouter = express.Router();

  // Setup auth routes
  var callBACkUrl = '/oauth/callBACk';
  var loginUrl    = '/login';

  authRouter.get(callBACkUrl,.... });
  authRouter.get(loginUrl,function(req,res,next){
    // Make call to OAuth server
    res.redirect("http://authserver/?callBACk=" + callBACkUrl);
  });

  return authRouter;
}

问题是authRouter不知道它实际上是在/ admin下安装的,因此它无法将其添加到回调参数中.

有什么方法可以在getAuthRouter函数中得到它吗？