GoogleActions Account not linked yet error – Facebook api

I’m trying to implement oauth2 authentication on my nodejs Google Assistant app developed using (DialogFlow or API.ai and google actions).

So I followed this answer. But I’m always getting “It looks like your test oauth account is not linked yet. ” error. When I tried to open the url shown on the debug tab, it shows 500 broken url error.

Dialogflow fullfillment

index.js

'use strict';

const functions = require('firebase-functions'); // Cloud Functions for Firebase library
const DialogflowApp = require('actions-on-google').DialogflowApp; // Google Assistant helper library

const googleAssistantRequest = 'google'; // Constant to identify Google Assistant requests

exports.dialogflowFirebaseFulfillment = functions.https.onRequest((request, response) => {
  console.log('Request headers: ' + JSON.stringify(request.headers));
  console.log('Request body: ' + JSON.stringify(request.body));

  // An action is a string used to identify what needs to be done in fulfillment
  let action = request.body.result.action; // https://dialogflow.com/docs/actions-and-parameters

  // Parameters are any entites that Dialogflow has extracted from the request.
  const parameters = request.body.result.parameters; // https://dialogflow.com/docs/actions-and-parameters

  // Contexts are objects used to track and store conversation state
  const inputContexts = request.body.result.contexts; // https://dialogflow.com/docs/contexts

  // Get the request source (Google Assistant, Slack, API, etc) and initialize DialogflowApp
  const requestSource = (request.body.originalRequest) ? request.body.originalRequest.source : undefined;
  const app = new DialogflowApp({request: request, response: response});

  // Create handlers for Dialogflow actions as well as a 'default' handler
  const actionHandlers = {
    // The default welcome intent has been matched, welcome the user (https://dialogflow.com/docs/events#default_welcome_intent)
    'input.welcome': () => {
      // Use the Actions on Google lib to respond to Google requests; for other requests use JSON
      //+app.getUser().authToken
      if (requestSource === googleAssistantRequest) {
        sendGoogleResponse('Hello, Welcome to my Dialogflow agent!'); // Send simple response to user
      } else {
        sendResponse('Hello, Welcome to my Dialogflow agent!'); // Send simple response to user
      }
    },
    // The default fallback intent has been matched, try to recover (https://dialogflow.com/docs/intents#fallback_intents)
    'input.unknown': () => {
      // Use the Actions on Google lib to respond to Google requests; for other requests use JSON
      if (requestSource === googleAssistantRequest) {
        sendGoogleResponse('I'm having trouble, can you try that again?'); // Send simple response to user
      } else {
        sendResponse('I'm having trouble, can you try that again?'); // Send simple response to user
      }
    },
    // Default handler for unknown or undefined actions
    'default': () => {
      // Use the Actions on Google lib to respond to Google requests; for other requests use JSON
      if (requestSource === googleAssistantRequest) {
        let responseToUser = {
          //googleRichResponse: googleRichResponse, // Optional, uncomment to enable
          //googleOutputContexts: ['weather', 2, { ['city']: 'rome' }], // Optional, uncomment to enable
          speech: 'This message is from Dialogflow's Cloud Functions for Firebase editor!', // spoken response
          displayText: 'This is from Dialogflow's Cloud Functions for Firebase editor! :-)' // displayed response
        };
        sendGoogleResponse(responseToUser);
      } else {
        let responseToUser = {
          //richResponses: richResponses, // Optional, uncomment to enable
          //outputContexts: [{'name': 'weather', 'lifespan': 2, 'parameters': {'city': 'Rome'}}], // Optional, uncomment to enable
          speech: 'This message is from Dialogflow's Cloud Functions for Firebase editor!', // spoken response
          displayText: 'This is from Dialogflow's Cloud Functions for Firebase editor! :-)' // displayed response
        };
        sendResponse(responseToUser);
      }
    }
  };

  // If undefined or unknown action use the default handler
  if (!actionHandlers[action]) {
    action = 'default';
  }

  // Run the proper handler function to handle the request from Dialogflow
  actionHandlers[action]();

  // Function to send correctly formatted Google Assistant responses to Dialogflow which are then sent to the user
  function sendGoogleResponse (responseToUser) {
    if (typeof responseToUser === 'string') {
      app.ask(responseToUser); // Google Assistant response
    } else {
      // If speech or displayText is defined use it to respond
      let googleResponse = app.buildRichResponse().addSimpleResponse({
        speech: responseToUser.speech || responseToUser.displayText,
        displayText: responseToUser.displayText || responseToUser.speech
      });

      // Optional: Overwrite previous response with rich response
      if (responseToUser.googleRichResponse) {
        googleResponse = responseToUser.googleRichResponse;
      }

      // Optional: add contexts (https://dialogflow.com/docs/contexts)
      if (responseToUser.googleOutputContexts) {
        app.setContext(...responseToUser.googleOutputContexts);
      }

      app.ask(googleResponse); // Send response to Dialogflow and Google Assistant
    }
  }

  // Function to send correctly formatted responses to Dialogflow which are then sent to the user
  function sendResponse (responseToUser) {
    // if the response is a string send it as a response to the user
    if (typeof responseToUser === 'string') {
      let responseJson = {};
      responseJson.speech = responseToUser; // spoken response
      responseJson.displayText = responseToUser; // displayed response
      response.json(responseJson); // Send response to Dialogflow
    } else {
      // If the response to the user includes rich responses or contexts send them to Dialogflow
      let responseJson = {};

      // If speech or displayText is defined, use it to respond (if one isn't defined use the other's value)
      responseJson.speech = responseToUser.speech || responseToUser.displayText;
      responseJson.displayText = responseToUser.displayText || responseToUser.speech;

      // Optional: add rich messages for integrations (https://dialogflow.com/docs/rich-messages)
      responseJson.data = responseToUser.richResponses;

      // Optional: add contexts (https://dialogflow.com/docs/contexts)
      responseJson.contextOut = responseToUser.outputContexts;

      response.json(responseJson); // Send response to Dialogflow
    }
  }
});

// Construct rich response for Google Assistant
const app = new DialogflowApp();
const googleRichResponse = app.buildRichResponse()
  .addSimpleResponse('This is the first simple response for Google Assistant')
  .addSuggestions(
    ['Suggestion Chip', 'Another Suggestion Chip'])
    // Create a basic card and add it to the rich response
  .addBasicCard(app.buildBasicCard(`This is a basic card.  Text in a
 basic card can include "quotes" and most other unicode characters
 including emoji 📱.  Basic cards also support some markdown
 formatting like *emphasis* or _italics_, **strong** or __bold__,
 and ***bold itallic*** or ___strong emphasis___ as well as other things
 like line  nbreaks`) // Note the two spaces before 'n' required for a
                        // line break to be rendered in the card
    .setSubtitle('This is a subtitle')
    .setTitle('Title: this is a title')
    .addButton('This is a button', 'https://assistant.google.com/')
    .setImage('https://developers.google.com/actions/images/badges/XPM_BADGING_GoogleAssistant_VER.png',
      'Image alternate text'))
  .addSimpleResponse({ speech: 'This is another simple response',
    displayText: 'This is the another simple response 💁' });

// Rich responses for both Slack and Facebook
const richResponses = {
  'slack': {
    'text': 'This is a text response for Slack.',
    'attachments': [
      {
        'title': 'Title: this is a title',
        'title_link': 'https://assistant.google.com/',
        'text': 'This is an attachment.  Text in attachments can include 'quotes' and most other unicode characters including emoji 📱.  Attachments also upport linenbreaks.',
        'image_url': 'https://developers.google.com/actions/images/badges/XPM_BADGING_GoogleAssistant_VER.png',
        'fallback': 'This is a fallback.'
      }
    ]
  },
  'facebook': {
    'attachment': {
      'type': 'template',
      'payload': {
        'template_type': 'generic',
        'elements': [
          {
            'title': 'Title: this is a title',
            'image_url': 'https://developers.google.com/actions/images/badges/XPM_BADGING_GoogleAssistant_VER.png',
            'subtitle': 'This is a subtitle',
            'default_action': {
              'type': 'web_url',
              'url': 'https://assistant.google.com/'
            },
            'buttons': [
              {
                'type': 'web_url',
                'url': 'https://assistant.google.com/',
                'title': 'This is a button'
              }
            ]
          }
        ]
      }
    }
  }
};

Actually I deployed the code exists in the dialog flow inline editor. But don’t know how to implement an oauth endpoint, whether it should be a separate cloud function or it has to be included within the existsing one. And also I am so confused with how oauth authorization code flow will actually work.. Let’s assume we are on the Assistant app, once the user say “talk to foo app”, does it automatically opens a web browser for oauth code exchange process?