Easy Facebook Conversations without Webhook : /graph.facebook.com/v2.12 [step by step]

index.js

var request = require('request');
var express = require('express');
var app = express();
var session = require('express-session');

var FB_PAGE_ID = '<FB_PAGE_ID>';
var sess = {
  secret: 'keyboard cat',
  cookie: {},
  resave: true,
  saveUninitialized: true
}
 
if (app.get('env') === 'production') {
  app.set('trust proxy', 1) // trust first proxy 
  sess.cookie.secure = true // serve secure cookies 
}
var OAuth2 = require('oauth').OAuth2;
var oauth2 = new OAuth2("<FB_APP_ID>",
                        "<FB_APP_SECRET>",
                        "", "https://www.facebook.com/dialog/oauth",
                        "https://graph.facebook.com/oauth/access_token",
                        null );
app.use(session(sess));
app.get('/facebook/auth',function (req, res) {
      var redirect_uri = "http://localhost:3000/facebook/callback";
      // For eg. "http://localhost:3000/facebook/callback"
      var params = {'redirect_uri': redirect_uri, 'scope':'user_about_me,publish_actions,pages_messaging,manage_pages,pages_show_list,read_page_mailboxes '};
      var rr = oauth2.getAuthorizeUrl(params);
      console.log(rr);
      res.redirect(rr);
});

app.get("/facebook/callback", function (req, res) {
    if (req.error_reason) {
        return res.send(req.error_reason);
    }
    if (req.query.code) {
        var loginCode = req.query.code;
        var redirect_uri = 'http://localhost:3000/facebook/callback'; // Path_To_Be_Redirected_to_After_Verification
        // For eg. "/facebook/callback"
        var access_token, expires;
        oauth2.getOAuthAccessToken(loginCode, { grant_type: 'authorization_code', redirect_uri: redirect_uri}, 
            function(err, accessToken, refreshToken, params){
                if (err) {
                    console.error(err);
                    return res.send({'err':err.msg});
                }
                access_token = accessToken;
                expires = params.expires;
                req.session.access_token = access_token;
                req.session.expires = expires;
                return res.send({'access':access_token, 'expires': expires});
            }
        );
    }
});

// get id cua page FB
app.get('/page_token', function(req, res) {
    oauth2.get('https://graph.facebook.com/me/accounts', req.session.access_token, function(err, data ,response) {
        if (err) {
            console.error(err);
            return res.send(err);
        } else {
			var x = JSON.parse(data);
			var b = x.data.filter(e=> e.id==FB_PAGE_ID)[0];
			req.session.page_token = b['access_token'];
			req.session.page_id = b.id;
			console.log(req.session);
            return res.send(x);
        }
    });
});

// get messages of page: conversations
app.get('/page_action', function(req, res) {
    var url = 'https://graph.facebook.com/v2.12/'+req.session.page_id+'/conversations';
	var opts= '\?fields=messages{message,from}';
	url+= opts;
    oauth2.get(url, req.session.page_token, function(err, data ,response) {
        if (err) {
            console.error(err);
            return res.send(err);
        } else {
            var profile = JSON.parse(data);
            return res.send(profile);
        }
    });
});

app.get('/all', function(req, res) {
	return res.send(req.session);
});

app.set('port', (process.env.PORT || 3000));
app.listen(app.get('port'));

1. http://localhost:3000/facebook/auth
2. code-granting
3. redirect callback url: http://localhost:3000/facebook/callback -> generation access_token
4. generate page_access_token with access_token: http://localhost:3000/page_token
5. read conversations.. http://localhost:3000/page_action