Cannot execute https request in ssr

Question

I am running a very annoying error with https calls from the server. The error Http failure response for (unknown url): 0 Unknown Error.

In my angular application, I make an https call when it is executed in the browser, everything is fine, but when this call is made on the server, I get an error. This is a complete error:

HttpErrorResponse {
headers: HttpHeaders { normalizedNames: Map {}, lazyUpdate: null, 
headers: Map {} },
  status: 0,
  statusText: 'Unknown Error',
  url: null,
  ok: false,
  name: 'HttpErrorResponse',
  message: 'Http failure response for (unknown url): 0 Unknown Error',
  error:
   ProgressEvent {
     type: 'error',
     target:
      XMLHttpRequest {
        onloadstart: null,
        onprogress: null,
        onabort: null,
        onerror: null,
        onload: null,
        ontimeout: null,
        onloadend: null,
        _listeners: [Object],
        onreadystatechange: null,
        _anonymous: undefined,
        readyState: 4,
        response: null,
        responseText: '',
        responseType: 'json',
        responseURL: '',
        status: 0,
        statusText: '',
        timeout: 0,
        upload: [Object],
        _method: 'GET',
        _url: [Object],
        _sync: false,
        _headers: [Object],
        _loweredHeaders: [Object],
        _mimeOverride: null,
        _request: null,
        _response: null,
        _responseParts: null,
        _responseHeaders: null,
        _aborting: null,
        _error: null,
        _loadedBytes: 0,
        _totalBytes: 0,
        _lengthComputable: false },
     currentTarget:
      XMLHttpRequest {
        onloadstart: null,
        onprogress: null,
        onabort: null,
        onerror: null,
        onload: null,
        ontimeout: null,
        onloadend: null,
        _listeners: [Object],
        onreadystatechange: null,
        _anonymous: undefined,
        readyState: 4,
        response: null,
        responseText: '',
        responseType: 'json',
        responseURL: '',
        status: 0,
        statusText: '',
        timeout: 0,
        upload: [Object],
        _method: 'GET',
        _url: [Object],
        _sync: false,
        _headers: [Object],
        _loweredHeaders: [Object],
        _mimeOverride: null,
        _request: null,
        _response: null,
        _responseParts: null,
        _responseHeaders: null,
        _aborting: null,
        _error: null,
        _loadedBytes: 0,
        _totalBytes: 0,
        _lengthComputable: false },
     lengthComputable: false,
     loaded: 0,
     total: 0 } }

The certificate of my server and the called server are reliable and valid. This is my server code:

import 'reflect-metadata';
import 'zone.js/dist/zone-node';
import { renderModuleFactory } from '@angular/platform-server';
import { enableProdMode } from '@angular/core';
import * as express from 'express';
import { join } from 'path';
import { readFileSync } from 'fs';
import './global.imports';
import * as https from 'https';

enableProdMode();

const PORT = Number(process.env.PORT) || 4001;
const HOST_NAME = process.env.HOST;

const DIST_FOLDER = join(process.cwd(), 'dist');

const app = express();

const template = readFileSync(join(DIST_FOLDER, 'browser', 'index.html')).toString();
const {AppServerModuleNgFactory} = require('main.server');

app.engine('html', (_, options, callback) => {
  const opts = {document: template, url: options.req.url};

  renderModuleFactory(AppServerModuleNgFactory, opts)
    .then(html => callback(null, html));
});

app.set('view engine', 'html');
app.set('views', 'src');

app.get('*.*', express.static(join(DIST_FOLDER, 'browser')));

app.get('*', (req, res) => {
  res.render('index', {req});
});

const privateKey = readFileSync(`${DIST_FOLDER}/server/config/ssl/key.pem`, 'utf8');
const certificate = readFileSync(`${DIST_FOLDER}/server/config/ssl/cert.pem`, 'utf8');

const credentials = {key: privateKey, cert: certificate};

// your express configuration here

const httpsServer = https.createServer(credentials, app);

httpsServer.listen(PORT, HOST_NAME, () => {
  console.log(`listening to https://${HOST_NAME}:${PORT}`);
});

This is an obvious problem with https, because if I put this env variable before starting, everything will work NODE_TLS_REJECT_UNAUTHORIZED=0, but this is not a solution, because in this way I will disable security.

How can I solve this problem?