chain_http_rx.js

var rp = require('request-promise'),
    Rx = require('rx')

const uriAuthToken = 'https://login.windows.net/[YOUR_TENANT].onmicrosoft.com/oauth2/token'
const uriResource = 'http://[YOUR_RESTRICTED_RESOURCE]'

const optionsAuthToken = {
  method: 'POST',
  uri: uriAuthToken,  
  form: {
    grant_type: 'password',
    scope: 'openid',
    resource: 'http://samplewebservice.azure-mobile.net', //If you follow my example
    client_id: 'client-id-of-the-AAD-native-app',
    username,
    password
  },
  json: true
}

const observable = Rx.Observable.fromPromise(rp(optionsAuthToken))
.map(response => {
  const optionsResource = {
    uri: uriResource,
    headers: {
      authorization: response.token_type + ' ' + response.access_token
    },
    json: true
  }  
  
  return Rx.Observable.fromPromise(rp(optionsResource))
})
.flatMap(item => item)


observable.subscribe(response => {
  console.log(response)
}, error => {
  console.log("an error occurred", error, error.message, error.stack)
})